Abstract
A high resolution cavity ringdown spectrometer (CRDS) has been constructed using a 1.5 μm continuous-wave external-cavity tunable diode laser, a mode-matched near-confocal ringdown cavity, and 2 cm pulsed slit jet. Without signal averaging, the RMS noise in the absorption signal is 1.7 × 10 −9 cm −1. The rotationally resolved overtone spectrum of the OH( ν 1) + CH( ν 3) stretch combination band of methanol between 6510 and 6550 cm −1 has been observed for J ′=0–8 and K ′=0–3 at sub-Doppler resolution. In total, 418 lines are assigned and global fits yield molecular torsion–rotation parameters for the upper state. Four K ′-localized perturbations are analyzed and the pattern of residuals is discussed.
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