Abstract: We present in this paper new and updated calculations of the ionization equilibrium for all the elements from H to Ni. We collected for these elements all the data available in the literature for the ionization and radiative plus dielectronic recombination rates. In particular, the dielectronic rates have been fitted with a single formula and the related coefficients are tabulated. Our results are compared with previous works.

Abstract: We present in this paper new and updated calculations of the ionization equilibrium for all the elements from H to Ni. We collected for these elements all the data available in the literature for the ionization and radiative plus dielectronic recombination rates. In particular, the dielectronic rates have been fitted with a single formula and the related coefficients are tabulated. Our results are compared with previous works.

Abstract: The origin of ions in matrix-assisted laser desorption/ionization (MALDI) mass spectrometry is currently a matter of active research A number of chemical and physical pathways have been suggested for MALDI ion formation, including gas-phase photoionization, ion–molecule reactions, disproportionation, excited-state proton transfer, energy pooling, thermal ionization, and desorption of preformed ions These pathways and others are critically reviewed, and their varying roles in the wide variety of MALDI experiments are discussed An understanding of ionization pathways should help to maximize ion yields, control analyte charge states and fragmentation, and gain access to new classes of analytes © 1999 John Wiley & Sons, Inc Mass Spec Rev 17: 337–366, 1998

Abstract: A set of 146 well-established ionization potentials and electron affinities is presented. This set, referred to as the G2 ion test set, includes the 63 atoms and molecules whose ionization potentials and electron affinities were used to test Gaussian-2 (G2) theory [J. Chem. Phys. 94, 7221 (1991)] and 83 new atoms and molecules. It is hoped that this new test set combined with the recently published test set of enthalpies of neutral molecules [J. Chem. Phys. 106, 1063 (1997)] will provide a means for assessing and improving theoretical models. From an assessment of G2 and density functional theories on this test set, it is found that G2 theory is the most reliable method. It has an average absolute deviation of 0.06 eV for both ionization potentials and electron affinities. The two modified versions of G2 theory, G2(MP2,SVP) and G2(MP2) theory, have average absolute deviations of 0.08–0.09 eV for both ionization potentials and electron affinities. The hybrid B3LYP density functional method has the smallest...

Abstract: The degree of ionization, x(e) = n(e)/n(H2), and the cosmic-ray ionization rate, ζ, in 24 cloud cores have been determined by comparing observational data from Butner et al. on the abundance ratios RD = [DCO+]/[HCO+] and RH = [HCO+]/[CO] with a simple analytical chemical model and with a detailed "pseudo-time-dependent" chemical model. The results are dependent on the depletion of elemental carbon and oxygen from their cosmic abundances, especially for cores with a low degree of ionization. We determine the depletion of C and O from the measured HC3N/CO abundance ratios using model results. We find that the range of fractional ionization in the dark cores extends from ~10-6 to ~10-8, with inferred cosmic ray ionization rates in the range of 10-16-10-18 s-1. This corresponds to ambipolar diffusion timescales of between 3 × 107 and 3 × 105 yr, with a median value of 5 × 106 yr. The ratio of ambipolar diffusion to the free-fall timescales varies between 3 and 200, with a median value of 50. We find, rather surprisingly, no clear segregation in the ambipolar diffusion timescales between cores with embedded stars and those without. An interesting by-product of our results is the conclusion that the cyanopolyyne-rich core in TMC-1 is atypical in its abundance distribution and may be unusually young.

Abstract: A model of the density distribution in the intergalactic medium, motivated by that found in numerical simulations, is used to demonstrate the effect of a clumpy IGM and discrete sources on the reionization of the universe. In an inhomogeneous universe reionization occurs outside-in, starting in voids and gradually penetrating into overdense regions. Reionization should not be sudden but gradual, with a continuous rise of the photon mean free path over a fair fraction of the Hubble time as the emissivity increases. We show that a hydrogen Gunn-Peterson trough should be present at $z\simeq 6$ unless the emissivity increases with redshift at $z>4$. However, the epoch of overlap of cosmological \hii regions could have occurred at a higher redshift if sources of low luminosity reionized the IGM; the Gunn-Peterson trough at $z\sim 6$ would then appear because even the most underdense voids have a large enough neutral fraction in ionization equilibrium to be optically thick to \lya photons. Cosmological \hii regions near the epoch of overlap can produce gaps of transmitted flux only if luminous quasars contributed to the reionization. Despite the clumpiness of the matter distribution, recombinations are not very important during the reionization of hydrogen because the high density gas is not ionized until a late time. We show that the \heii reionization was most likely delayed relative to the hydrogen reionization, but should be completed by $z\sim 3$, the redshift where observations are available. The reported large optical depth fluctuations of \heii are probably not due to an incomplete \heii reionization, but arise from a combination of density fluctuations and the variations in the intensity of the ionizing background due to luminous QSO's.

Abstract: The time-dependent Schr\"odinger equation for the one-dimensional ${\mathrm{H}}_{2}^{+}$ molecule (with both nuclear and electronic degrees of freedom included) was solved numerically to study dissociative ionization. A wave-function splitting technique was used with projections onto Volkov states, which allows one to circumvent the problem of lost information on electron flux due to absorbing boundary methods. This technique allows us to calculate the above-threshold ionization (ATI) photo electron kinetic-energy spectra in the presence of moving nuclei, as well as complete spectra of dissociating protons, beyond the Born-Oppenheimer approximation. The ATI spectra are considerably enhanced with respect to the H-atom spectra due to electron molecule interaction. The peaks seen in calculated Coulomb explosion spectra of protons agree well with recent theoretical and experimental work related to the phenomenon of charge-resonance-enhanced ionization in molecules.

Abstract: Using data from the Voyager and Pioneer spacecraft at distances up to 60 AU from the Sun to help define the effects of solar modulation, we have made a new estimate of the local interstellar cosmic-ray spectra and the associated energy density and ionization rate. The energy density, including the low-energy electron contribution, is ~1.80 eV cm-3, equivalent energetically to that in a 7 μG magnetic field. The ionization rate from this same cosmic-ray population, including a significant contribution from low-energy electrons, is (3-4) × 10-17 s-1 (H atom). This is most likely a minimum value and is not too different from estimates of the typical ionization rate required to heat the interstellar medium and maintain the diffuse ionized gas range from (3-30) × 10-17 s-1 (H atom) as a function of locale in the Galaxy. This suggests that cosmic rays could be a significant contributor to interstellar heating. The cosmic-ray ionization rate will be more or less uniform throughout the Galactic disk and also perpendicular to the disk according to the scale height of cosmic rays which may be ~1 kpc, thus providing a source of ionization at high Z values. The recent observation of low-energy particle acceleration at the heliospheric termination shock, which produces local ionization rates comparable to those due to Galactic cosmic rays, raises the interesting possibility that "hot spots," where the ionization rate due to locally accelerated particles may exceed 10-16 s-1 (H atom), may occur near massive stars with more powerful stellar winds.

Abstract: Preface to the Second Edition. Acknowledgments. Abbreviations and Notations Used in This Book. 1. Instrumentation. 1.1. Introduction. 1.1.1. Overview. 1.1.2. Sample Introduction. 1.2. Ionization Source. 1.2.1. Electron Ionization Source. 1.2.2. Chemical Ionization. 1.2.3. Other Ionization Methods. 1.2.3.1. Electrospray Ionization. 1.2.3.2. Desorption Ionization. 1.3. m/z Analysis. 1.3.1. Time-of-Flight (TOF). 1.3.2. Magnetic Sector. 1.3.3. Transmission Quadrupole. 1.3.3.1. Selected Ion Monitoring (SIM). 1.3.4. Quadrupole Ion Trap (QIT). 1.3.5. Other Types of Mass Analysis. 1.3.5.1. Mass Spectrometry/Mass Spectrometry(MS/MS). 1.3.5.2. Accurate m/z Analysis. 1.3.6. Spectral Skewing. 1.4. Ion Detection. 1.4.1. Electron Multiplier. 1.4.2. Photomultiplier Detector. 1.5. Data System. 1.5.1. Instrument Tuning and Calibration. 1.5.2. The Mass Spectrum. 1.5.2.1. Production of the Mass Spectrum. 1.5.2.2. Terminology: Ions vs. Peaks. 1.5.3. Library Searches. 1.5.4. Using the Data System to Analyze GC/MS Data. 1.6. Criteria for Good-Quality Spectra. Additional Problems. Mass Spectrometric Resources on the Internet. References and Suggested Reading. 2. Elemental Composition from Peak Intensities. 2.1. Natural Isotopic Abundances. 2.1.1. Atomic and Molecular Mass. 2.1.2. Calculated Exact Masses and Mass Defects. 2.2. Determining Elemental Composition from Isotope Peak Intensities. 2.2.1. One or More Atoms of a Single Element. 2.2.1.1. Chlorine and Bromine. 2.2.1.2. Ion Designation and Nomenclature. 2.2.1.3. Probability Considerations with Multiple Numbers of Atoms. 2.2.1.4. Isotope Peak Intensity Ratios for Carbon-Containing Ions-The X + 1 Peak. 2.2.1.5. A, A + 1, and A + 2 Elements. 2.2.1.6. Isotope Peak Intensity Ratios for Carbon-Containing Ions-The X + 2 Peak. 2.2.1.7. Overlapping Peak Clusters-Contributions from 13C Only. 2.2.1.8. Silicon. 2.2.2. Complex Isotope Clusters. 2.2.2.1. Sulfur Dioxide. 2.2.2.2. Diazepam. 2.3. Obtaining Elemental Compositions from Isotope Peak Intensities. Examples. Additional Problems. References. 3. Ionization, Fragmentation, and Electron Accounting. 3.1. A Brief Review of Orbitals and Bonding. 3.2. Even- and Odd-Electron Species. 3.3. Site of Initial Ionization. 3.4. Types of Fragmentation. 3.5. The Nitrogen Rule. 3.6. Energy Considerations in Fragmentation Processes. 3.6.1. Fragmentation Rates. 3.6.2. Metastable Ions. 3.6.3. Energy Diagrams. 3.6.4. Stevenson's Rule. Additional Examples. Problems. References. 4. Neutral Losses and Ion Series. 4.1. Neutral Losses. 4.1.1. Losses from the Molecular Ion. 4.1.2. Loss of Small Molecules from Aromatic Ions. 4.2. Low-Mass Ion Series. 4.2.1. n-Alkane Spectra. 4.2.2. Effect of Chain Branching on the Spectra of Aliphatic Hydrocarbons. 4.2.3. Ion Series for Nonaromatic Compounds. 4.2.4. Aromatic Ion Series. 4.2.5. Use of Ion Series: Mass Chromatograms. Additional Problems. References. 5. A Rational Approach to Mass Spectral Problem Solving. 5.1. Guidelines for Solving Mass Spectral Problems. Examples. Problems. Reference. 6. a-Cleavage and Related Fragmentations. 6.1. Introduction. 6.2. Benzylic Cleavage. 6.3. Cleavage Next to Aliphatic Nitrogen. 6.3.1. Structural Relationships: a-Cleavage in 1-Phenyl-2-aminopropanes. 6.3.2. Cleavage Next to Electron-Deficient Nitrogen. 6.3.3. a-Cleavage in Complex Nitrogenous Ring Systems. 6.4. Cleavages of Aliphatic Oxygenated Compounds. 6.4.1. a-Cleavage. 6.4.2. Bond Cleavage Away from the Ionization Site. 6.4.3. Cleavage at Carbonyl Groups. 6.5. Elimination Fragmentations in Oxygen and Nitrogen Compounds . 6.5.1. Secondary Elimination from Initial a-Cleavage Ions. 6.5.2. Hydride Shifts. 6.5.3. Elimination Fragmentations of Some Aromatic Compounds. 6.5.4. Water Elimination in Aliphatic Alcohols. Examples. Additional Problems. References. 7. Important Mass Spectral Rearrangements. 7.1. Introduction. 7.2. gamma-Hydrogen Rearrangement. 7.2.1. McLafferty-Type Rearrangement. 7.2.2. gamma-Hydrogen Rearrangement in Alkylbenzenes. 7.2.3. gamma-Hydrogen Rearrangement Initiated by a Remote Ionization Site. 7.3. Cyclohexanone-Type Rearrangement. 7.4. Retro Diels-Alder Fragmentation. 7.5. Double-Hydrogen (McLafferty t 1) Rearrangement. Additional Problems. References. 8. Rationalizing Mass Spectral Fragmentations. 8.1. General Guidelines. 8.2. Loss of Small Molecules. 8.2.1. Loss of Small Molecules from Aromatic Ions Revisited. 8.2.2. gamma-Butyrolactone. 8.3. Ephedrine. 8.4. Ortho Effect: The Hydroxybenzoic Acids. Additional Problems. References. 9. Structure Determination in Complex Molecules Using Mass Spectrometry. 9.1. Introduction. 9.2. "Designer Drugs" Related to MDA. 9.3. Cocaine and Its Metabolites. 9.3.1. Peak Correlations. 9.3.2. Proposed Fragmentations. 9.3.3. Application. 9.4. Phencyclidine and Its Analogs. 9.4.1. Fragmentations of Phencyclidine. 9.4.2. Phencyclidine Analogs. 9.5. A Practical Problem. References. 10. Answers to Problems. Index.

Abstract: Multiple ionization of neon, argon and xenon in a high-intensity Ti:Sapphire laser field has been studied Ion yield curves of xenon versus laser intensity have been obtained for the first six charges Curves of charges 2+ to 6+ present obvious structures which can be attributed to the occurrence of non-sequential ionization processes Also, comparison of the ion yields of the first three charges of Ar with previously obtained results inside a different laser field (Nd:Glass laser , ) indicates that non-sequential ionization is strongly wavelength dependent

Abstract: A three-dimensional plasma model was developed to understand the sources and sinks that maintain Europa's neutral atmosphere and to study the interaction of the Jovian magnetosphere with this atmosphere and the formation of an ionosphere. The model includes self-consistently the feedback of the plasma action on the atmosphere through mass balance. Suprathermal torus ions with a contribution from thermal ions sputter O 2 from the water ice surface, and thermal torus ions remove the O 2 atmosphere by sputtering. For an oxygen column density of 5 × 10 18 m -2 the calculated intensities of the oxygen lines OI 130.4 nm and 135.6 nm produced by electron impact dissociation agree with observations by the Hubble Space Telescope [Hall et al., 1995]. Mass balance is also consistent with this column density, with a net atmospheric mass loss of 50 kg s -1 . For a given neutral atmosphere and magnetospheric conditions, the electrodynamic model computes self-consistently plasma density, plasma velocity, electron temperature of the thermal and the suprathermal population, electric current and electric field in the vicinity of Europa, with the assumption of a constant homogeneous Jovian magnetic field. Europa's ionosphere is created by electron impact ionization where the coupling of the ionosphere with the energy reservoir of the plasma torus by electron heat conduction supplies the energy to maintain ionization. The calculated distribution of electron densities with a maximum value of nearly 10 4 cm -3 is in general agreement with densities derived by Kliore et al. [1997] from the Galileo spacecraft radio occultations. The Alfvenic current system closed by the ionospheric Hall and Pedersen conductivities carries a total current of 7 × 10 5 A in each Alfven wing.

Abstract: This work is the first of two companion papers devoted to the kinetic modelling of low-pressure DC flowing discharges in - mixtures. While the present paper is mainly concerned with bulk discharge processes, the second one investigates surface processes involving dissociated N and H atoms, which are essential to understand the discharge properties. The global model combining bulk and surface processes as described in these two papers is self-contained in the sense that the sole input parameters it requires are those that can externally be chosen in experiments, namely: total gas pressure, radius and length of the discharge tube, discharge current, gas flow rate and initial gas temperature and composition (e.g., the relative hydrogen concentration X in the binary mixture at the discharge inlet). For a given set of input parameters, this model enables one to calculate the following bulk plasma properties as a function of the axial coordinate z: concentration of , , NH, , molecules and N, H atoms in the ground electronic state; population in the electronically excited states , (an effective high Rydberg state) and ; concentration of the ions , , , , , and ; vibrational level populations of and molecules; electron density , mean kinetic energy , characteristic energy and drift velocity ; discharge sustaining electric field E; average gas temperature across the tube T and wall temperature . The calculations are compared with data from different experiments in pure and discharges (measurements of electric field as a function of current and pressure) and in - discharges (measurements of relative changes in the electric field and the , concentrations as a function of the percentage). From the comparison to experiment, rate coefficients for associative ionization upon collisions between two excited molecules and deactivation of and by H atoms have been estimated from the model.

Abstract: The methyl iodide A-band photodissociation process CH3I+hν→CH3(v,N,K)+I(2P3/2), I*(2P1/2) has been studied in a cold molecular beam. Full three-dimensional state-specific speed and angular distributions of the nascent fragments were recorded using (2+1) resonance-enhanced multi-photon ionization (REMPI) and velocity imaging, a new variant of ion imaging. By combining the I* quantum yield and anisotropy parameters for both I and I* channels, the relative absorption strength to the contributing electronic states (3Q0, 3Q1 and 1Q1) as well as the probability for curve crossing (3Q0→1Q1) are determined for excitation wavelengths across the full A band (240–334 nm). Parallel excitation to the 3Q0 state turns out to dominate the A band even more than previously thought.

Abstract: Interaction of low-energy ions with solids sputtering of multicomponent materials ionization processes at surfaces ion bombardment of crystalline semiconductors.

Abstract: Experimental and theoretical data on tunneling and barrier-suppression ionization of atoms and atomic ions in a low-frequency laser radiation field are considered. The yields of single- and multi-charged ions, the energy and angular distributions of photoelectrons, and effects of the laser pulse length and laser polarization are analyzed.

Abstract: Observations of C18O, H13CO+, and DCO+ toward 23 low-mass cores are used to constrain the fractional ionization (electron abundance) within them. Chemical models have been run over a wide range of densities, cosmic-ray ionization rates, and elemental depletions, and we find that we can fit 20 of the 23 cores for densities of nH2=(1-3)×104 cm-3, moderate C and O abundance variations, and a cosmic-ray ionization rate of ζH2=5×10−17 s-1. The derived ionization fractions lie within the range 10-7.5 to 10-6.5, with a median value of xe,m = 9 × 10-8 and typical errors for each individual core equal to a factor of 3. These values imply that the cores are weakly coupled to the magnetic field and that MHD waves can propagate within them. The ambipolar diffusion timescale is about an order of magnitude greater than the free-fall time, and the cores can be considered to be in quasi-static equilibrium. There is no significant difference between the ionization fraction for cores with and without embedded stars, which suggests that the molecular ionization in cores is primarily governed by cosmic rays alone.

Abstract: Atomic clusters have long been studied by chemists and physicists because of the unique position that clusters hold as an intermediate state between molecules and solids [1]. Many studies have traced the properties of materials from their monatomic characteristics to their bulk state characteristics through an examination of the material as it forms larger and larger clusters. Recently, there has been much activity in extending these studies to very high intensity, ultrashort laser pulses with peak laser intensities >1015 Wcm −2 and pulse widths of 0.1 to 10 ps [2–11]. There has also been some preliminary theoretical work in this area as well [6,12]. In this parameter regime the physics governing the laser cluster interaction is fundamentally different than in previous studies. At these intensities the laser interaction is non-perturbative and very high order multiphoton ionization and strong electric field tunnel ionization are possible. Consequently, highly charged ions can be produced [2,5,8,10]. Furthermore, the short pulses used are comparable to or shorter than the disassembly times of a cluster in the laser field [6] and, so, the entire laser pulse interacts with an inertially confined body of atoms.

Abstract: ?????Metal line ratios in a sample of 13 quasar spectra obtained with the HIRES spectrograph on the Keck I Telescope have been analyzed to characterize the evolution of the metagalactic ionizing flux near a redshift of 3. The evolution of Si IV/C IV has been determined using three different techniques: using total column densities of absorption-line complexes, as in the approach of Songaila & Cowie, using the column densities of individual Voigt profile components within complexes, and using direct optical depth ratios. All three methods show that Si IV/C IV changes abruptly at z ~ 3, requiring a jump in value of about a factor of 3.4 and indicating a significant change in the ionizing spectrum that occurs rapidly between z = 2.9 and z = 3, just above the redshift at which Reimers et al. detected patchy He II Ly? absorption. At lower redshifts, the ionization balance is consistent with a pure power-law ionizing spectrum, but at higher redshifts the spectrum must be very soft, with a large break at the He+ edge. An optical depth ratio technique is used to measure the abundances of ions whose transitions lie within the forest, and C III, Si III, and O VI are detected in this way. The presence of a significant amount of O VI at z > 3 suggests either a considerable volume of He III bubbles embedded in the more general region in which the ionizing flux is heavily broken or the addition of collisional ionization to the simple photoionization models.

Abstract: The internal energy deposited in the ions in the source of a mass spectrometer governs their fragmentation and therefore the content of the spectra. When the ionization conditions are well defined and reproducible, e.g. in electron impact, the elaboration of databases benefits the use of the method. In electrospray, however, the source conditions are not strictly defined. The elaboration of spectra databases therefore requires a calibration of the internal energy of the ions that is valid for all types of spectrometers. A method for the calibration of the internal energy of ions in electrospray is presented, developed using the fragmentation reactions of a set of probe ions (benzylpyridinium salts) under various conditions (the voltage on the sampling cone, the nature of the collision gas, the composition of the mobile phase). The influence of the experimental conditions on the internal energy of the ions permits the calibration of individual working conditions. © 1998 John Wiley & Sons, Ltd.

Abstract: A recently developed form of threshold ionization spectroscopy has been used to determine the bond energy for HCl to spectroscopic accuracy (±0.8 cm−1). This method is based on excitation to highly vibrationally excited ion-pair states using single-photon transitions from the ground state of HCl. These metastable Rydberg-like states were selectively detected using electricfield induced dissociation. By systematically varying the electric fields involved, and scanning the exciting photon energy, it was possible to determine the field-free energetic threshold for H35Cl+hν→H++35Cl−. Using this energy, together with the known values of the ionization potential of H and electron affinity of Cl, a new estimate for the dissociation energy of HCl was obtained: D0(H35Cl)=35 748.2±0.8 cm−1.

Abstract: The nature of the optical--radio correlations for powerful radio galaxies is investigated using spectroscopic observations of a complete sample of southern 2Jy radio sources. In line with previous work, we find that significant correlations exist between the luminosities of the [OIII]5007, [OII]3727 and Hbeta emission lines and the radio luminosity. However, our observations are not easily reconciled with the idea that these correlations are caused by the increase in the power of the photoionizing quasar as the jet power increases, with average ISM properties not changing appreciably with redshift or radio power: not only do we find that the scatter in the L_[OIII] vs. L_radio correlation is significantly larger than in L_[OII]} vs. L_radio and L_Hbeta vs. L_radio correlations, but the ionization state deduced from the emission lines does not increase with radio power as predicted by the simple, constant ISM, photionization model. We conclude that: (a) there exists a considerable range in the quasar ionizing luminosity at a given redshift; and (b) that the mean density of the emission line clouds is larger in the high redshift/high power radio sources. The latter density enhancement may either be a consequence of the increased importance of jet-cloud interactions or, alternatively, due to a higher pressure in the confining hot ISM, in the high redshift objects. Deep spectra show that many of the sources in our sample are broad line radio galaxies (BLRG). The fact that the BLRG are observed out the redshift limit of the survey, overlapping in redshift with the quasars, argues against the idea that BLRG are simply the low radio power counterparts of high power, high redshift quasars.

Abstract: Measurements of above-threshold ionization electron spectra in an elliptically polarized field as a function of the ellipticity are presented. In the rescattering regime, electron yields quickly drop with increasing ellipticity. The yields of lower-energy electrons rise again when circular polarization is approached. A classical explanation for these effects is provided. Additional local maxima in the yields of lower-energy electrons can be interpreted as being due to interferences of electron trajectories that tunnel out at different times within one cycle of the field.

Abstract: The temperature and ionization of SN 1987A are modeled time-dependently in its nebular phase between 200 and 2000 days. We include all important elements, as well as the primary composition zones in the supernova. The energy input is provided by radioactive decay of 56Co,57Co, and 44Ti. The thermalization of the resulting gamma-rays and positrons is calculated by solving the Spencer-Fano equation. Both the ionization and the individual level populations are calculated time-dependently. Adiabatic cooling is included in the energy equation. Charge transfer is important for determining the ionization, and is included with available and estimated rates. Full, multilevel atoms are used for the observationally important ions. As input models for the calculations we use explosion models for SN 1987A calculated by Woosley et al. and Nomoto et al. The most important result in this paper concerns the evolution of the temperature and ionization of the various abundance zones. The metal-rich core undergoes a thermal instability, often referred to as the IR catastrophe, at 600-1000 days. The hydrogen-rich zones evolve adiabatically after 500-800 days, while in the helium region both adiabatic cooling and line cooling are of equal importance after ~1000 days. Freezeout of the recombination is important in the hydrogen and helium zones. Concomitant with the IR catastrophe, the bulk of the emission shifts from optical and near-IR lines to the mid- and far-IR. After the IR catastrophe, the cooling is mainly due to far-IR lines and adiabatic expansion. Dust cooling is likely to be important in the zones where dust forms. We find that the dust condensation temperatures occur later than ~500 days in the oxygen-rich zones, and that the most favorable zone for dust condensation is the iron core. The uncertainties introduced by the (in some cases) unknown charge transfer rates are discussed. Especially for ions with low abundances, differences can be substantial.

Abstract: Photoionization spectroscopy has been used to probe molecular beams of laser-vaporized chromium (Cr2) and molybdenum (Mo2) dimers. Two-color photoionization efficiency spectroscopy has been used to determine the adiabatic ionization potential (IP) of Cr2 and Mo2 to be 56 449±8 cm−1 and 56 042±8 cm−1, respectively. The IP of Cr2 is combined with the IP of Cr [54 575.6±0.3 cm−1, Huber et al., Proc. R. Soc. London, Ser. A 342, 431 (1975)] and the bond energy of Cr2+ [10 200±500 cm−1, Su et al., Chem. Phys. Lett. 201, 199 (1993)] to yield a bond energy of 12 400±500 cm−1 for Cr2. One-color resonant two-photon ionization (R2PI) spectroscopy has been employed to probe the molybdenum dimer molecule in the energy region where its dissociation should occur. The dissociation limit has been ascribed to the threshold observed at 36 100±80 cm−1. This value is combined with the IP of Mo [57 204.3±0.3 cm−1, Rayner et al., J. Opt. Soc. Am. B 4, 900 (1987)] and Mo2 to yield a bond energy of 37 260±80 cm−1 for Mo2+.

Abstract: The effect of ion drag on negatively charged dust grains is considered as a possible mechanism of excitation of the dust-acoustic (DA) ionization instability. It is found that DA waves are more and more damped as the coefficient for ion drag, μ, increases from zero to a critical value, μcrit. For μ>μcrit a zero-frequency (nonpropagating) perturbation grows when the drag of the ions on the dust grains overcomes the effect of the perturbation electric field.

Abstract: The photoelectron spectra for benzene, naphthalene, and anthracene ionized using a 780 nm, 170 fs laser pulse of intensity $3.8\ifmmode\times\else\texttimes\fi{}{10}^{13}\mathrm{W}{\mathrm{cm}}^{\ensuremath{-}2}$ reveal a decrease in the discrete features associated with above threshold ionization with increasing molecular size. A corresponding exponential increase in the intensity of a broad featureless distribution indicates that field ionization dominates the coupling mechanism for the larger molecules. A coupling model based on a zero-range potential predicts that only multiphoton ionization should occur. This model, incorporating both the ionization potential and electronic delocalization of the molecule, correctly predicts the observed transition.