Absolute line strengths in nu(4), (12)CH(4): a dual-beam diode laser spectrometer with sweep integration.
A tunable diode laser spectrometer with several unique features has been developed for use in the middle IR. The all-reflective optical system has a dual-beam configuration before the dispersive mode selector to eliminate transit-angle errors at the calibration etalon. By maintaining separated beams through the mode selector, beam combiner losses are avoided. Averaging successive sweeps of the current-modulated laser permits stable reproducible spectral integrations, eliminating etalon thermal errors and producing high photometric sensitivity. Line strengths have been measured using this instrument for eleven transitions in nu(4) of (12)CH(4). These include R0 and R1 and nine P-branch transitions in the 1202-1263-cm(-1) range. Techniques for measuring strengths with a diode laser are discussed.
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Jennings