Photodetachment spectroscopy and resonant photoelectron imaging of the 2-naphthoxide anion via dipole-bound excited states

Abstract

We report a photodetachment spectroscopy and high-resolution resonant photoelectron imaging study of cryogenically cooled 2-naphthoxide anions (C10H7O-). The photodetachment spectrum revealed a dipole-bound state (DBS) 202(4) cm-1 below the detachment threshold and 38 resonances corresponding to the vibrational levels of the DBS. By tuning the detachment laser to these above-threshold resonances, we obtained 38 resonantly enhanced photoelectron spectra, which were highly non-Franck-Condon as a result of mode-selective vibrational autodetachment from the DBS. The resonances were assigned by comparing the resonant and non-resonant photoelectron spectra, assisted by the computed vibrational frequencies. Specifically, vibrational features with low Franck-Condon factors or from Franck-Condon-forbidden vibrational modes were significantly enhanced in the resonant photoelectron spectra, resulting in much richer spectroscopic information. The electron affinity of the 2-naphthoxy radical was measured accurately to be 19 387(4) cm-1 or 2.4037(5) eV. In addition, a total of 17 vibrational frequencies were obtained for the 2-naphthoxy radical. In particular, seven Franck-Condon-forbidden out-of-plane bending modes, including the two lowest frequency modes (ν48 at 102 cm-1 and ν47 at 171 cm-1), were observed, demonstrating the advantages of combining photodetachment spectroscopy and resonant photoelectron spectroscopy in obtaining vibrational information for polar radical species via DBS.