Investigation of the ν2 + 2ν3 Subband in the Overtone Icosad of 13CH4 by Pulsed Supersonic Jet and Diode Laser Cavity Ring-Down Spectroscopy: Partial Rovibrational Analysis and Nuclear Spin Symmetry Conservation

Abstract

We have investigated the v2 +2v3 combination band of methane13CH4centered at7493.15918 cm−1within the icosad of the overtone absorption. Thejet-CRD setup combining supersonic jet expansions and cavity ring-down spec-troscopy which was already used for the reinvestigation of the same spectral re-gion for the main isotope of methane (12CH4) has been used to record spectraof the Q and R branches at room temperature as well as at very low temperatures(down to4K). Based on our previous temperature-dependent investigations andthe present results, we provide a careful analysis and the assignment for lines in-volving angular momentum quantumnumbers up to J=4. The analysisof the rel-ative intensities in spectra taken at various rotational and effective translationaltemperatures demonstrate conservation of nuclear spin symmetry for13CH4un-der the conditions of asupersonic jet expansion, similar to our previous resultsregarding12CH4and also to further results using other techniques and coveringother spectral ranges. This is in agreement with theoretical expectation regardingvery slow nuclear spin symmetry relaxation under these conditions in supersonicjet expansions.