Color center lasers

Mesure de la reponse transitoire de CO excite de facon vibrationnelle adsorbe sur la surface Pt(111). Le declin du signal de blanchiment transitoire est interprete comme donnant un temps T 1 pour l'amortissement de CO. L'absorption transitoire est discutee en termes de transitions de l'adsorbat excite aux niveaux d'harmoniques

Ultrafast infrared response of adsorbates on metal surfaces: Vibrational lifetime of CO/Pt(111).

Vibrational spectra of CO physisorbed onto well defined NaCl(100) surfaces were studied using a Fourier transform infrared interferometer. Structures of CO starting from the monolayer to multilayers were explored. At 31.5 K and a CO pressure of 1×10−6 mbar only the monolayer is formed. Polarization measurements confirm our earlier study that the monolayer CO molecules are aligned perpendicular to the NaCl(100) surface. Increasing the CO pressure to 7×10−6 mbar produces multilayer adsorption. The multilayer spectra closely resemble that of α‐CO absorption previously reported. The near perfect match of crystal structures and lattice constants of α‐CO and NaCl is reasoned to force the epitaxial growth of single crystal multilayers in our experiments. At 22 K the monolayer absorption is at 2155.01 cm−1 with a bandwidth (FWHH) of 0.26 cm−1. The two prominent features in the multilayer spectra at 22 K are assigned to the longitudinal optical (LO) mode at 2142.54 cm−1 and the transverse optical (TO) mode at 2138...

Epitaxial growth of CO on NaCl(100) studied by infrared spectroscopy

A potential force field has been evaluated for the calculation of the properties of the solid CO-Ar system. The CO·Ar potential energy has been expressed as a sum of the C·Ar and O·Ar interatomic interactions. The (6-exp) Buckingham form of the atom—atom potential, ϕ = − Ar −6 + B exp (−α r ), has been used ( r is the interatomic distance). The values of the A, B and α numerical parameters for the C·Ar and O·Ar potential have been obtained from those for the C·C, O·O, and Ar·Ar potentials using known combining rules. These values are the following: A C·Ar = 3379 kJ/mol A 6 , B C·Ar = 3.12 × 10 5 kJ/mol, α C·Ar = 3.493 A −1 , A O·Ar = 2737 kJ/mol A 6 , B O·Ar = 3.28 × 10 5 kJ/mol, α O·Ar = 3.706 A −1 . The three parameters of the Ar·Ar potential function ( A Ar·Ar = 6554 kJ/mol A 6 , B Ar·Ar = 3.27 × 10 5 kJ/mol, α Ar·Ar = 3.305 A −1 ) have been fitted to a set of experimental data for the Ar crystal (zero-temperature lattice spacing and energy, and the value of the isothermal compressibility). The CO·Ar potential surface has been calculated showing the most favourable position of an Ar atom near the CO molecule and the orientational dependence of the CO·Ar interactions. The CO·Ar separation distance at the potential minimum and the depth of the potential well are equal to 3.63 A and −1.321 kJ/mol, respectively. Comparison has been made of the derived Ar·Ar and Co·Ar potential functions with other such functions available in the literature.

Carbon monoxide molecules in an argon matrix: empirical evaluation of the Ar·Ar, C·Ar and O·Ar potential parameters

Temperature and time effects on the rovibrational structure of fundamentals of H2O trapped in solid argon: hindered rotation and RTC satellite

The infrared emission of CO trapped in solid Ne and Ar is observed at low temperature. The first vibrational level of 12 C 16 O is excited by a Q -switched frequency doubled CO 2 laser. The emission spectrum consists of several lines arising from upper vibrational levels of 12 C 16 O and also of 13 C 16 O and 12 C 18 O which are present in natural abundance. An interpretation is proposed which is based on the assumption that long range dipole—dipole interaction is the main physical process involved in these experiments. Resonance energy transfer produces an energy migration among 12 C 16 O molecules without any change in vibrational populations. Phonon assisted energy transfer takes place between vibrational levels of the various isotopic species present in the solution. In order to satisfy the resonance condition a phonon is emitted or absorbed whose energy compensates for the energy mismatch between the transitions in each interacting molecule due to isotopic effect and or vibrational anharmonicity. The range of this process is greatly extended by energy migration. At the low phonon bath temperature phonon emission is much more probable than phonon absorption. So a strong excitation of upper vibrational levels with in some cases population inversions is observed. Molecular impurities act as efficient quenching centers even at very low concentration. When highly purified samples are used, the fluorescence decay time is found to be 20.6 ms in Ne and 14.5 ms in Ar and does not significantly depend upon concentration and temperature. It is concluded that radiationless relaxation is unimportant.

Laser studies of vibrational energy transfer and relaxation of CO trapped in solid neon and argon

Librational relaxation and IR line broadening of matrix isolated CO

IR-induced UV-visible fluorescence in matrix-isolated CO

Nitric oxide dispersed in solid argon and krypton is vibrationally excited by a cw modulated infrared laser resonant with the fundamental or first overtone absorption. The energy deposited into ν = 1 or ν = 2 is redistributed to higher levels by intermolecular vibration to vibration transfer. The vibrational population distributions obtained from overtone emission spectra in both IR and visible regions or probed using a pulsed dye laser extend over a broad range. The topmost detected level is ν = 27. In addition to the vibrational fluorescence, electronic luminescence emanating from the lowest excited valence states a 4 Π and B 2 Π of NO is found to be induced by IR laser irradiation. The slow irreversible decay of the electronic emissions followed by thermoluminescence shows that a small fraction of the NO molecules is dissociated. Time and frequency resolved analysis of the various emissions is performed as a function of the relevant parameters. The results show that X 2 Π→a 4 Π intersystem crossing and X 2 Π→B 2 Π internal conversion do not occur in matrix isolated NO. A new mechanism of intermolecular vibrational to electronic energy transfer involving the exchange “en bloc” of a large number of vibrational quanta between highly vibrationally excited molecules is proposed. The excitation of NO to predissociated vibronic levels of the B 2 Π state results in electronic emission and dissociation.

Intermolecular transfer of vibrational energy in matrix isolated NO. High vibrational states, electronic excitation and dissociation

IR stimulated emission on the 2 → 1 vibrational transition of no in solid N2

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