Abstract
Threshold photodetachment spectroscopy of the molecular ion has been performed at both 16(1) and 295(2) K in a 22-pole ion trap. The 295(2) K spectrum shows a large increase in the cross section with an onset about below threshold, which is explained by significant vibrational excitation of the trapped ions at room temperature. This excitation disappears at cryogenic temperatures leading to an almost steplike onset of the cross section at threshold, which cannot be adequately described with a Wigner threshold law. Instead, we show that the model developed by O’Malley for photodetachment from neutrals with large permanent dipoles [Phys. Rev. 137, A1668 (1965)] fits very well to the data. A high-resolution scan of the threshold region yields additional features, which we assign to the rotational and branches of an electronic transition to a dipole-bound state with symmetry. This state is found below threshold in very good agreement with a recent computational prediction. We furthermore refine the value of the electron affinity of to be .
- Received 5 February 2021
- Revised 28 April 2021
- Accepted 26 May 2021
DOI:https://doi.org/10.1103/PhysRevLett.127.043001
Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.
Published by the American Physical Society