Two-dimensional spectra of electron collisions with acrylonitrile and methacrylonitrile reveal nuclear dynamics

Abstract

Detailed experimental information on the motion of a nuclear packet on a complex (resonant) anion potential surface is obtained by measuring 2-dimensional (2D) electron energy loss spectra. The cross section is plotted as a function of incident electron energy, which determines which resonant anion state is populated, i.e., along which normal coordinate the wave packet is launched, and of the electron energy loss, which reveals into which final states each specific resonant state decays. The 2D spectra are presented for acrylonitrile and methacrylonitrile, at the incident energy range 0.095-1.0 eV, where the incoming electron is temporarily captured in the lowest π * orbital. The 2D spectra reveal selectivity patterns with respect to which vibrations are excited in the attachment and de-excited in the detachment. Further insight is gained by recording 1D spectra measured along horizontal, vertical, and diagonal cuts of the 2D spectrum. The methyl group in methacrylonitrile increases the resonance width 7 times. This converts the sharp resonances of acrylonitrile into boomerang structures but preserves the essence of the selectivity patterns. Selectivity of vibrational excitation by higher-lying shape resonances up to 8 eV is also reported.

High-resolution photoelectron imaging and resonant photoelectron spectroscopy via noncovalently bound excited states of cryogenically cooled anions

“…Hence, there is a nite probability for the outgoing electron to interact inelastically with the neutral core because of exciting low-frequency vibrational modes, akin to processes in electron energy loss spectroscopy. 90,91 Take Fig. 9b as an example: autodetachment from the DBS vibrational level 16 01 (n 16 ¼ 577 cm À1 , Table 1) of [U-H] À yields an outgoing photoelectron with a kinetic energy of 431 cm À1 by subtracting the 146 cm À1 binding energy of the DBS.…”

Dissociative electron attachment and electronic excitation in Fe(CO)5

“…Two-dimensional (2D) spectra provide insight into the dynamics of resonances by mapping their decay channels and their capacity to thermalize electrons. [44][45][46] The 2D spectrum of Fe(CO) 5 is shown in Fig. 9.…”

Structure Optimization of Temporary Anions

“…Electron energy loss (EEL) spectroscopy on acrylonitrile and methacrylonitrile indicates the presence of three low-lying π* resonances . The lowest anionic states of both molecules feature rich vibrational structure in the EEL spectra so that the AEAs corresponding to these states can be determined experimentally. , The experimental data suggest that the anion of methacrylonitrile has a considerably shorter lifetime than that of acrylonitrile.…”

“…Hence, complex-valued PES (CPES) can be constructed for an anion at molecular structures where it is not bound but of temporary nature. CPES can be experimentally probed, for example, in electron impact, − electron transmission, − and photodetachment experiments. Temporary anions can be observed as resonances in such spectra with the spectral width corresponding to their inverse lifetime.…”