Related Experiment Video
Updated: May 18, 2026

Measuring Dissolved Methane in Aquatic Ecosystems Using An Optical Spectroscopy Gas Analyzer
Published on: July 26, 2024
Spectroscopic isotope ratio measurement of doubly-substituted methane
Kiyoshi Tsuji1, Hiroaki Teshima, Hiroyuki Sasada
1Interdisciplinary Graduate School of Science and Engineering, Tokyo Institute of Technology, Yokohama 226-8502, Japan. ktsuji@depe.titech.ac.jp
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.
Related Concept Videos
Mass Spectrometry: Isotope Effect
Mass Spectrum
Mass Spectrum: Interpretation
Chemical Ionization (CI) Mass Spectrometry
¹³C NMR: Distortionless Enhancement by Polarization Transfer (DEPT)
Mass Spectrometry: Long-Chain Alkane Fragmentation

