High-Resolution Photoelectron Spectroscopy of Vibrationally Excited Vinoxide Anions.

ABSTRACT

High-resolution photoelectron spectra of vibrationally pre-excited vinoxide anions (CH2CHO-) are reported using the recently developed IR-cryo-SEVI technique. This method is combined with a newly developed implementation of vibrational perturbation theory that can readily identify relevant anharmonic couplings among nearly degenerate vibrational states. IR-cryo-SEVI spectra are obtained by resonant infrared excitation of vinoxide anions via the fundamental C-O (ν4, 1566 cm-1) or isolated C-H (ν3, 2540 cm-1) stretching vibrations prior to photodetachment. Excitation of the ν4 mode leads to a well-resolved photoelectron spectrum that is in excellent agreement with a harmonic Franck-Condon simulation. Excitation of the higher-energy ν3 mode results in a more complicated spectrum that requires consideration of the calculated anharmonic resonances in both the anion and the neutral. From this analysis, information about the zeroth-order states that contribute to the nominal ν3 wave function in the anion is obtained. In the neutral, we observe anharmonic splitting of the ν3 fundamental into a polyad feature with peaks at 2737(22), 2 835(18), and 2910(12) cm-1, for which only the center frequency has been previously reported. Overall, 9 of the 12 fundamental frequencies of the vinoxy radical are extracted from the IR-cryo-SEVI and ground-state cryo-SEVI spectra, most of which are consistent with previous measurements. However, we provide a new estimate of the ν5 (CH2 scissoring) fundamental frequency at 1395(11) cm-1 and attribute the discrepancy with previously reported values to a Fermi resonance with the 2ν11 overtone (CH2 wagging).