Vibrational state-selective autodetachment photoelectron spectroscopy from dipole-bound states of cold 2-hydroxyphenoxide: o-HO(C6H4)O(-).

We report a photodetachment and high-resolution photoelectron imaging study of cold 2-hydroxyphenoxide anion, o - HO(C6H4)O(-), cooled in a cryogenic ion trap. Photodetachment spectroscopy revealed a dipole-bound state (DBS) of the anion, 25 ± 5 cm(-1), below the detachment threshold of 18 784 ± 5 cm−1 (2.3289 ± 0.0006 eV), i.e., the electron affinity of the 2-hydroxyphenoxy radical o - HO(C6H4)O(⋅). Twenty-two vibrational levels of the DBS are observed as resonances in the photodetachment spectrum. By tuning the detachment laser to these DBS vibrational levels, we obtain 22 high-resolution resonant photoelectron spectra, which are highly non-Franck-Condon due to mode-selective autodetachment and the Δv = - 1 propensity rule. Numerous Franck-Condon inactive vibrational modes are observed in the resonant photoelectron spectra, significantly expanding the vibrational information that is available in traditional high-resolution photoelectron spectroscopy. A total of 15 fundamental vibrational frequencies are obtained for the o - HO(C6H4)O(⋅)  radical from both the photodetachment spectrum and the resonant photoelectron spectra, including six symmetry-forbidden out-of-plane modes as a result of resonant enhancement.