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Abstract
High-resolution photoelectron spectra of vibrationally pre-excited vinoxide anions (CH2CHOβ) 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 (π4, 1570 cmβ1) or isolated C-H (π3, 2546 cmβ1) stretching vibrations prior to photodetachment. Excitation of the π4 mode leads to a well-resolved photoelectron spectrum that is in excellent agreement with a harmonic Franck-Condon simulation. Excitation of the higher energy π3 mode results in a more complicated spectrum that requires consideration of the calculated anharmonic resonances in both the anion and neutral. From this analysis, information about the zeroth-order states that contribute to the nominal π3 wavefunction in the anion is obtained. In the neutral, we observe anharmonic splitting of the π3 fundamental into a polyad feature with peaks at 2737(22), 2835(18) and 2910(12) cmβ1, for which only the center frequency has been previously reported. Overall, nine out of the twelve 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 π5 (CH2 scissoring) fundamental frequency at 1395(11) cmβ1 and attribute the large difference with previously reported values to a Fermi resonance with the 2π11 overtone (CH2 wagging).
Supplementary materials
Title
Supporting Information
Description
Additional experimental and theoretical details: details of the anharmonic Franck-Condon simulations (Section S1), a description of the βweighted FC spectraβ method (Section S2), experimental setup (Figure S1), normal modes (Figures S2 and S3), FC simulations for different frequency shifts (Figures S4 and S5), anisotropy parameters (Figure S6), infrared action spectra (Figure S7), weighted FC spectra (Figures S8 and S9), Optimized geometries in valence (Table S1) and Cartesian coordinates (Table S2), anion π3 coupling and coefficient matrices (Tables S3 and S4), fundamental frequencies used in eBE calculations for the π3 simulations (Table S5), neutral π5 coupling and coefficient matrices (Tables S6 and S7).
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Title
Coupling and coefficient matrices
Description
Coupling and coefficient matrices for the anion and neutral π3 fundamentals and neutral π5 fundamental.
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