Velocity Map Imaging Spectroscopy of the Dipole-Bound State of CH<sub>2</sub>CN<sup>–</sup>: Implications for the Diffuse Interstellar Bands
Benjamin Laws, Zachariah D. Levey, Timothy W. Schmidt, S. T. Gibson
Abstract
Weakly bound anionic systems present a new domain for negative ion spectroscopy. Here we report on a multifaceted study of the CH2CN– dipole-bound state, employing high-resolution photoelectron spectroscopy from 130 different wavelengths, velocity-map imaging at threshold, and laser scanning photodetachment experiments. This uncovers a wide variety of different vibrational and rotational autodetaching resonances. By examination of both sides of the problem, absorption from the anion to the dipole-bound state and vibrational/rotational autodetachment to the neutral, a complete model of the dipole-bound chemistry is formed. Precise values for the electron affinity EA = 12468.9(1) cm–1, dipole binding energy DBE = 40.2(3) cm–1, and anion inversion splitting ω5 = 115.9(2) cm–1 are obtained. This model is then employed to study possible astronomical implications, revealing good agreement between the K = 1 ← 0 CH2CN– dipole transition and the λ8040 diffuse interstellar band.