Survey of Ar-Tagged Predissociation and Vibrationally Mediated Photodetachment Spectroscopies of the Vinylidene Anion, C2H2

We report predissociation spectra of Ar-tagged C2H2 − and C2D2 − anions, and explore vibrationally mediated photodetachment from various vibrational levels of the bare C2H2 − ion using velocity-map imaging. Intense photodetachment resonances are observed in the C−H stretching region that are strongly correlated with vibrational hot bands in the anion photoelectron spectra, indicating that one-color, resonant two-photon photodetachment (R2PD) is complicated by excitation of vibrationally excited states with autodetaching upper levels embedded in the continuum. Isolation of the R2PD spectrum was achieved using a two-color, IR−IR scheme in which vibrational excitation and photodetachment were carried out in two separate laser interaction regions.