Interdisciplinary Graduate School of Science and Engineering, Tokyo Institute of Technology, Yokohama 226-8502, Japan.
Spectrochim Acta A Mol Biomol Spectrosc. 2012 Dec;98:43-6. doi: 10.1016/j.saa.2012.08.028. Epub 2012 Aug 19.
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.
我们使用灵敏的差频发生光谱仪在 3.4μm 区域，以 ~20‰ 的不确定度确定了 (13)CH(3)D/(12)CH(3)D 和 (13)CH(3)D/(12)CH(4)的同位素比值。通过冷却吸收池，大大减少了 (13)CH(3)D 谱线与其他丰度同位素谱线的重叠，光谱仪的广泛可调谐性使我们能够获得适合同位素比值测量的跃迁对。我们测量了 (13)CH(3)D ν(4)(R)P (7, 0)线、(12)CH(3)D 2ν(5)(R)Q (9, 0)线和 (12)CH(4)ν(2)+ν(4) R(10) F(2)线在 2953cm(-1)处的强度，以及 (13)CH(3)D ν(4)(P)P (6, 3)线和 (12)CH(4)ν(3) P (6)E 线在 2955cm(-1)处的强度，因为它们具有相似的跃迁频率、吸收强度和低态能量。
