title: Spectroscopic isotope ratio measurement of doubly-substituted methane.
abstract: We have determined the isotope ratios of (13)CH(3)D /(12)CH(3)D as well as (13)CH(3)D /(12)CH(4) with an uncertainty of ~20‰ using a sensitive difference-frequency-generation spectrometer in the 3.4 μm region. Cooling the absorption cell drastically reduces overlap of the (13)CH(3)D lines with the other abundant isotopic lines, and the extensive tunability of the spectrometer enables us to access transition pairs appropriate for isotope ratio measurements. We measure the intensity of the (13)CH(3)D ν(4)(R)P (7, 0) line, the (12)CH(3)D 2ν(5)(R)Q (9, 0) line, and the (12)CH(4)ν(2)+ν(4) R(10) F(2) line at 2953 cm(-1) as well as the (13)CH(3)D ν(4)(P)P (6, 3) line and the (12)CH(4)ν(3) P (6) E line at 2955 cm(-1) because they have similar transition frequencies, absorption strengths, and low state energies.
authors.affiliation: Interdisciplinary Graduate School of Science and Engineering, Tokyo Institute of Technology, Yokohama 226-8502, Japan. ktsuji@depe.titech.ac.jp
authors.forename: Kiyoshi
authors.initials: K
authors.lastname: Tsuji
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Teshima
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Sasada
authors.forename: Naohiro
authors.initials: N
authors.lastname: Yoshida
mesh_terms: D003903:Deuterium / Q000737:chemistry; D007834:Lasers; D008697:Methane / Q000737:chemistry*; D008958:Models, Molecular; D013057:Spectrum Analysis / Q000379:methods; D013696:Temperature
chemical_list: D003903:Deuterium; D008697:Methane