~Received 28 December 1995; accepted 9 May 1996! Conventional ~valence! and dipole-bound anions of the nitromethane molecule are studied using negative ion photoelectron spectroscopy, Rydberg charge exchange and field detachment techniques. Reaction rates for charge exchange between Cs(ns,nd) and Xe( nf ) Rydberg atoms with CH 3 NO 2 exhibit a pronounced maximum at an effective quantum number of n*’1361 which is characteristic of the formation of dipole-bound anions @m~CH 3 NO 2 !53.46 D#. However, the breadth ~Dn’5, FWHM! of the n-dependence of the reaction rate is also interpreted to be indicative of direct attachment into a valence anion state via a ‘‘doorway’’ dipole anion state. Studies of the electric field detachment of CH 3NO2 formed through the Xe( nf ) reactions at various n values provide further evidence for the formation of both a dipole-bound anion as well as a contribution from the valence bound anion. Analysis of the field ionization data yields a dipole electron affinity of 1263 meV. Photodetachment of CH3NO2 and CD3NO2 formed via a supersonic expansion nozzle ion source produces a photoelectron spectrum with a long vibrational progression indicative of a conventional ~valence bound! anion with a substantial difference in the equilibrium structure of the anion and its corresponding neutral. Assignment of the origin ~v850, v950! transitions in the photoelectron spectra of CH3NO2 and CD3NO2 yields adiabatic electron affinities of 0.2660.08 and 0.2460.08 eV, respectively. © 1996 American Institute of Physics.@S0021-9606~96!02831-0#

/pdf/on-the-binding-of-electrons-to-nitromethane-dipole-and-n730lrewhd.pdf

On the binding of electrons to nitromethane: Dipole and valence bound anions

The valence‐ and dipole‐bound states of CH3NO−2 are studied at the CCSD(T), HFDFT (B3LYP), and EA‐EOMCC levels of theory. At both CCSD(T) and HFDFT levels, we have found a positive valence EA in nice agreement with the experimental data. The binding energy of the dipole‐bound electron is about 13 meV according to the EA‐EOMCC calculations. Interaction of the valence‐ and dipole‐bound states (DBS) of CH3NO−2 is complicated, since the dipole‐bound state exists at the equilibrium geometry of the anion and corresponds to an excited state of the valence‐bound anion. Hence, excitations of the valence anionic state could lead to both the detachment of an electron or formation of a DBS, whose geometry is similar to the geometry of the neutral parent. At the equilibrium geometry of the anion, the energies of the dipole‐bound and valence states are close to each other. Since typical lifetimes of rovibrational excited states of a DBS are two orders of magnitude higher than the lifetimes of ordinary vibrationally exc...

A theoretical study of the valence‐ and dipole‐bound states of the nitromethane anion

The rate coefficients, beta , for the attachment reactions of electrons with c-C7F14, CH3Br, CF3Br, CH2Br2 and CH3I have been determined under truly thermal conditions at temperatures in the range 200-600K using the flowing afterglow/Langmuir probe technique. The beta values (in units of CM3 s-1) at 300K are 6.8*10-8, 6*10-12, 1.6*10-8, 9.3*10-8 and 1.2*10-7 respectively. The beta for all of the reactions increase with temperature and approach the theoretical maximum value of beta at high temperatures. From Arrhenius plots, activation energies for the reactions have been determined to be 40, 300, 80, 50 and 25 meV respectively. All of the reactions, except for that with c-C7F14 (for which electron attachment is apparently non-dissociative), proceed by exoergic dissociative attachment producing halogen atomic negative ions. The data are compared with previous data where these are available.

https://iopscience.iop.org/article/10.1088/0022-3700/17/18/019/pdf

Rate coefficients for the attachment reactions of electrons with c-C7F14, CH3Br, CF3Br, CH2Br2 and CH3I determined between 200 and 600K using the FALP technique

The negative ion products resulting from collisions between orthogonal beams of alkali atoms (Na, K, Cs) and the methane derivatives CH3CN, CH3NO2, CF3Br, and CF3I have been studied in the energy range from reaction thresholds to ∼40 eV (LAB). Stable negative ions with masses corresponding to the last three molecules were detected and the following electron affinities are derived from measurements of the energy threshold for the ion pair production reactions: E.A.(CH3NO2) =0.44+0.1−0.2 eV; E.A.(CF3Br) =0.91±0.2 eV, and E.A.(CF3I) =1.57±0.2 eV. From measurements of the difference between the energy threshold for the appearance of various fragment ions and the parent ion, the following bond dissociation energies are deduced: D(CH3–NO−2) =0.56±0.2 eV; D(CF3–Br−) =0.54±0.2 eV and D(CF3–I−) =0.32±0.2 eV. An argument is presented which adds further strength to the suggestions of Williams et al. and Jordan and Wendoloski that electron binding to CH3CN is dominated by the dipole field.

Collisional ionization between alkali atoms and some methane derivatives: Electron affinities for CH3NO2, CF3I, and CF3Br

Topics covered include: (1) modes of production of negative ions, (2) techniques for the study of electron attachment processes, (3) dissociative electron attachment to ground-state molecules, (4) dissociative electron attachment to hot molecules (effects of temperature on dissociative electron attachment), (5) molecular parent negative ions, and (6) negative ions formed by ion-pair processes and by collisions of molecules with ground state and Rydberg atoms.

Electron Attachment Processes

Thermal electron attachment to nitromethane, methylcyanide, methyliodide, and methylbromide is compared with capture of electrons by these molecules from highly excited Rydberg states of atoms. Data on thermal electron attachment to CH3NO2 are consistent with a three‐body attachment process, with the nature of the third body being important. The thermal energy electron attachment rate constant for CH3CN is ≤1.24×10−14 cm3 sec−1. Some results on dissociative electron attachment and ion pairing processes in CH3NO2, CH3CN, CH3I, and CH3Br are also presented.

Production of negative ions from CH3X molecules (CH3NO2, CH3CN, CH3I, CH3Br) by electron impact and by collisions with atoms in excited Rydberg states

Production of negative ions from CH$sub 3$X molecules (CH$sub 3$NO$sub 2$, CH$sub 3$CN, CH$sub 3$I, CH$sub 3$Br) by electron impact and by collisions with atoms in excited Rydberg states

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Production of negative ions from CH3X molecules (CH3NO2, CH3CN, CH3I, CH3Br) by electron impact and by collisions with atoms in excited Rydberg states

Production of negative ions from CH$sub 3$X molecules (CH$sub 3$NO$sub 2$, CH$sub 3$CN, CH$sub 3$I, CH$sub 3$Br) by electron impact and by collisions with atoms in excited Rydberg states