Sub-Doppler slit jet infrared spectroscopy of astrochemically relevant cations: The NH stretching mode in ND3H+

Author
Abstract
<p>High-resolution rotationally resolved spectra of the N\textendashH stretch vibrational mode (ν<sub>1</sub>) of jet-cooled ND<sub>3</sub>H<sup>+</sup>\&nbsp;ions are collected and analyzed in a sub-Doppler slit-jet infrared spectrometer. The isotopomeric ammonium ions are generated by proton transfer from H<sub>3</sub><sup>+</sup>\&nbsp;to ND<sub>3</sub>\&nbsp;in a discharge of an ND<sub>3</sub>/H<sub>2</sub>\&nbsp;gas mixture, whereby the slit jet expansion cools the nascent ND<sub>3</sub>H<sup>+</sup>\&nbsp;ions into lower rotational states. Rotational assignments are confirmed by four-line combination differences that agree to within the spectrometer precision (9 MHz). Based on precision two-line ground-state combination differences and a symmetric top Hamiltonian, the\&nbsp;B,\&nbsp;D<sub>J,</sub> and\&nbsp;D<sub>JK</sub>\&nbsp;rotational constants for the ground vibrational state of ND<sub>3</sub>H<sup>+</sup>\&nbsp;are determined with high precision for the first time. Approximate rotational constants for the\&nbsp;<em>ν</em><sub>1</sub>\&nbsp;excited state are also determined, with a band origin at 3316.8425(19) cm<sup>-1</sup>\&nbsp;and in remarkable (\~0.1 cm<sup>-1</sup>) agreement with high level anharmonic theoretical predictions by Guo and co-workers [J. Phys. Chem. A,\&nbsp;120, 2185 (2016)]. Our results allow us to predict several low-<em>J</em>\&nbsp;pure rotational transitions of ND<sub>3</sub>H<sup>+</sup>, which we hope will support future studies of this important ion in laboratory and astronomical rotational spectroscopy.</p>
Year of Publication
2018
Journal
The Journal of Chemical Physics
Volume
149
Number of Pages
144303
Date Published
2018-10
URL
https://aip.scitation.org/doi/full/10.1063/1.5049603
DOI
10.1063/1.5049603
JILA PI
Journal Article