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 Title: SUB-DOPPLER SPECTROSCOPY OF THE ν2 FUNDAMENTAL BAND AND FIRST HOT BAND OF THE H3+ CATION Author(s): Markus, Charles R. Contributor(s): McCall, Benjamin J.; Schrader, Alex W; Esposito, Anne Marie; Kocheril, Philip A. Subject(s): Mini-symposium: Frequency-Comb Spectroscopy Abstract: The simplest polyatomic molecule, \chem{H_3^+}, serves as an important benchmark for \textit{ab initio} theory and is an important constituent of the interstellar medium (ISM). In the ISM, \chem{H_3^+} initiates a chain of ion-neutral reactions which leads to more complex chemistry, and observations of \chem{H_3^+} can be used to measure interstellar conditions such as the cosmic ray ionization rate.\footnote{N. Indriolo, \textit{Phil. Trans. R. Soc. A}, \textbf{370}, 5142 (2012).} For \textit{ab initio} theorists, accurate calculations of the rovibrational structure of \chem{H_3^+} require going beyond the Born-Oppenheimer approximation, and for its low-lying rovibrational states, agreement between theory and experiment has reached 0.001 \wn.\footnote{L. G. Diniz, J. R. Mohallem, A. Alijah, M. Pavanello, L. Adamowicz, O. L. Polyansky, and J. Tennyson, \textit{Phys. Rev. A.}, \textbf{88}, 032506 (2013).} As these calculations begin to rival experimental measurements, new data are needed to benchmark future \textit{ab initio} approaches. Using the technique Noise-Immune Cavity-Enhanced Optical Heterodyne Velocity Modulation Spectroscopy (NICE-OHVMS)\footnote{J. N. Hodges, A. J. Perry, P. A. Jenkins II, B. M. Siller, and B. J. McCall, \textit{J. Chem. Phys}, \textbf{139}, 164201 (2013).} to perform sub-Doppler spectroscopy and an optical frequency comb to accurately calibrate the frequency, we have expanded our survey of \chem{H_3^+} to include transitions from higher rotational levels in the fundamental band and transitions in the $2\nu_2^2\leftarrow \nu_2^1$ hot band. Using combination differences, we have determined a number of energy level spacings in the ground state with an accuracy of $\sim 5$ MHz, which are directly compared with state of the art \textit{ab initio} calculations. We also discuss our progress towards calculating forbidden" rotational transitions, including a possible astrophysical maser,\footnote{J. H. Black, \textit{Phil. Trans. R. Soc. A}, \textbf{358}, 2515 (2000)} which requires our newly measured hot band transitions. Issue Date: 06/18/18 Publisher: International Symposium on Molecular Spectroscopy Citation Info: APS Genre: Conference Paper / Presentation Type: Text Language: English URI: http://hdl.handle.net/2142/100794 DOI: 10.15278/isms.2018.MG09 Other Identifier(s): MG09 Date Available in IDEALS: 2018-08-172018-12-12
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