Propensity rules for vibration-induced electron detachment of anions

Abstract

3971using high power pulsed lasers3394 is suitable for more conventional mass spectrometers in which ion-residence times arelod s. ciation of isomers often yields fragment ions in ratios that vary only slightly with the structure of the mecursor ion.z935 ~ -* Thus infrared photodissociation can be developed as a complementary technique to collisional activation for ion structure analysis. In particular, infrared excitation may be better suited to distinguish isomeric species because collision-induced disso-Acknowledgment. This work was supported by the United States Department Of Energy and the President's Fund Of the California Institute of Technology. We are grateful to Ms. Jocelyn Schultz for providing the photoelectron spectrum of c-C3F6. (34) Rosenfield, R. N.; Jasinski, J. M.; Brauman, J. I.Abstract: Vibration-induced detachment of electrons from molecular anions has recently been experimentally observed. In this paper, the coupling of the anion's vibration-rotation motion to its electronic degrees of freedom is analyzed in an attempt to predict under what circumstances efficient detachment would be expected. A set of propensity rules based upon the shapes of the anion and neutral potential-energy surfaces is put forth and applied to several prototypical situations. The development is not aimed at permitting ab initio calculations of electron detachment rates. Rather, it is designed to provide a useful tool both for interpreting experimental data and for designing especially interesting experiments to carry out.Recently it has been obsd.' that electrons can be detached from Abstract: Statistical mechanics simulations have been carried out for liquid dimethyl ether (DME) and methyl ethyl ether (MEE) at their boiling points and for liquid diethyl ether (DEE) at 25 OC. The intermolecular interactions were described by Coulomb and Lennard-Jones terms in the TIPS format. The internal rotations about the central CO bonds in the MEE and DEE monomers were also included, using potential functions derived from ab initio molecular orbital calculations. Optimization led to the interesting result that the dihedral angle for the gauche conformer in MEE occurs at ca. 85O in accord with electron diffraction data. A key finding is that the conformational equilibria for MEE and DEE are essentially unaffected by transfer from the gas phase to the pure liquids at the normal densities. The thermodynamic and detailed structural results for the liquids are also thoroughly analyzed. Excellent agreement is found with experiment for the computed heats of vaporization of all three liquids. A simulation of liquid DME under constant pressure conditions yielded a density within 4% of the experimental value which provides further support for the validity of the TIPS model. The liquids are disordered with high coordination numbers and no obvious repeating polymeric units. Trends in the structures and properties as a function of monomer size are discussed.

Autodetachment Dynamics of Acrylonitrile Anion Revealed by Two-Dimensional Electron Impact Spectra

“…With regard to the second question, Simons [12] showed that for a slightly unbound state like the present shape resonance two mechanisms may compete. One is via the direct electronic process, which involves a conventional anion-neutral Franck-Condon factor, weighted by how much the wave function of a given mode samples areas of the potential surface with large widths Γ(Q).…”

“…One approach to experimental study of autodetachment is based on vibrational photoexcitation of bound anions and detection of autodetached electrons [3][4][5][6][7][8], but the autodetaching anions can also be formed by electron attachment [9,10]. Various aspects of the theory were explained in the work of Simons [2,[11][12][13], with emphasis on vibrational autodetachment that requires inclusion of non-Born-Oppenheimer coupling, the theory of which has initially been inspired by the work on the related process of vibrational autoionization [14].…”

“…The ∆n = −1 processes (diagonals B and C) are much stronger than the ∆n = −2 processes, and thus follow the ∆n = ±1 rule. The propensity rules formulated for the non-BornOppenheimer route by Simons [1,2,12,13,33] are not easy to apply qualitatively to decide whether they can explain the striking ν 4 and ν 7 selectivity of the ∆n = −1 detachment.…”

A multi-agent quantum Monte Carlo model for charge transport: Application to organic field-effect transistors

“…In fact, a detachment spectrum was obtained by scanning the laser near the ν 11 vibrational levels and the ν 11 frequency measured for the DBS was found to be identical to that of the neutral phenoxy, as resolved in the PE spectra. Thus, there is a propensity rule of ∆v = −1 for the autodetachment, 151 first derived for autoionization of Rydberg states of H 2 . 152 The allowed and observed autodetachment channels are indicated in Fig.…”

Communication: Observation of dipole-bound state and high-resolution photoelectron imaging of cold acetate anions

“…Recently, we directly observed mode-specific vibrational autodetachment from DBSs of cold phenoxide anions, 36 which were cooled in a temperature-controlled ion trap to eliminate vibrational hot bands and minimize rotational broadening. The ∆v = −1 vibrational propensity rule, which was initially developed for autoionzation from Rydberg states 37 and extended to autodetachment, 38 was directly observed. More importantly, the vibrational frequencies of the DBS were measured to be the same as the neutral, suggesting the extra electron in the DBS of the anion has very little effect on the neutral core, analogous to a Rydberg state.…”