SUB-DOPPLER SPECTROSCOPY OF ND$_3$H$^{+}$ ION IN THE NH STRETCHING MODE
Loading...
Date
2013
Journal Title
Journal ISSN
Volume Title
Publisher
Ohio State University
Abstract
Despite early successes with velocity modulation spectroscopy$^{,}$of ammonium (NH$_4^{+}$ ) and perdeuteroammonium (ND$_4^{+}$) cation, corresponding studies of any of the mixed H/D isotopomers (NH$_m$D$_{4-m}^{+}$) have proven elusive. In this talk, we present first high resolution results on the lone NH stretch fundamental mode for the jet cooled ND$_3$H$^{+}$ ion, based on tunable IR difference frequency absorption spectroscopy in a slit jet, sub-Doppler resolution infrared spectrometer. Supersonically cooled ND$_3$H$^{+}$ ions are generated by modulated (50 KHz) discharges (650V, 500 mA) in ND$_3$ doped H$_2$/Ne slit jet expansions, monitored by time-gated, lock-in detection methods and with absorption sensitivities near the quantum shot noise limit. Jet cooled (30 K) $P$, $Q$, and $R$ branch rovibrational progressions in the $a$-type NH stretch band are observed and unambiguously assigned by four line ground state combination differences, with additional confirmation by nuclear spin statistical weights for the 3 identical D atoms (I = 1). Least squares fits to this parallel band yield precision rotational constants and an NH stretch vibrational band origin at 3316.8347(19) cm$^{-1}$. These high resolution spectroscopic results prove to be in generally excellent agreement with high level ${ab}$ initio theoretical predictions by Martin and Lee.
Description
Author Institution: JILA, National Institute of Standards and Technology; University of Colorado, and Department of Chemistry and Biochemistry; University of Colorado at Boulder, Colorado 80309