Stable isotopic analysis of atmospheric methane by infrared spectroscopy by use of diode laser difference-frequency generation.
An infrared absorption spectrometer has been constructed to measure the stable isotopic composition of atmospheric methane samples. The spectrometer employs periodically poled lithium niobate to generate 15 microW of tunable difference-frequency radiation from two near-infrared diode lasers that probe the nu3 rotational-vibrational band of methane at 3.4 microm. To enhance the signal, methane is extracted from 25 l of air by use of a cryogenic chromatographic column and is expanded into the multipass cell for analysis. A measurement precision of 12 per thousand is demonstrated for both delta13C and deltaD.
Trudeau
Michael E
ME
Earth System Research Laboratory, National Oceanic and Atmospheric Administration, Hilo, Hawaii 96720, USA. michael.trudeau@noaa.gov
Chen
Pin
P
Garcia
Guilherme de Andrade
Gde A
Hollberg
Leo W
LW
Tans
Pieter P
PP