Photodetachment Spectroscopy of—-CH2CN

Spectroscopic studies of the structure of negative ions exhibit two major limitations. Negative ions can be obtained in only very small densities compared to positive ions and neutrals (≲106 cm−3 for negative ions) [1]. In addition, the extra electron is usually bound by less than a few eV so that, in general, bound electronically excited states which would otherwise permit an electronic spectroscopic study of the ground state do not exist. The first problem can be avoided by using single particle detection of a transition, the second by several different t\ echioues: a) threshold photodetachment to the neutral [2]; b) infrared vibration-rotation spectroscopy [3]; c) excitation to an electronically excited negative ion above the detachment continuum and subsequent autodetachment [4—6]. The fact that any dipolar neutral molecule (≳2 Debye) can support an electronic state [7] has greatly facilitated the study of the ground and excited states of negative ions [5,6].