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FENG DONG, DAIRENE UY, SCOTT DAVIS, MARK CHILD AND DAVID J. NESBITT, JILA, University of Colorado, Boulder, CO 80309.
Jet-cooled high-resolution infrared spectra of partially deuterated hydronium ion, HD2O+ in the O-H stretch region (
3 band) are obtained for the first time, exploiting the high ion densities, long absorption path lengths, and concentration modulation capabilities of the slit jet discharge spectrometer. Least-square analysis with a Watson asymmetric top Hamiltonian yields rovibrational constants and provides high level tests of ab initio molecular structure predictions. Transitions out of both lower (
3+
0+) and upper (
3-
0-) tunneling levels are observed, as well as transitions across the tunneling gap (
3-
0+). The
3-
0+ transitions in HD2O+ acquire oscillator strength by loss of C3v symmetry and permit both ground (27.0318(72) cm-1) and excited state (17.7612(54) cm-1) tunneling splittings to be determined to spectroscopic precision from a single rovibrational band. The splittings and band origins calculated with recent high level ab initio 6D potential surface predictions for H3O+ and isotopomers are in very encouraging agreement with the current experimental results.