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arXiv · 1911.10592

High-resolution cavity ring-down spectroscopy of the $ν_1 + ν_6$ combination band of methanol at 2.0 $μ$m

Hongming Yi·Adam J. Fleisher
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Abstract

Reported here are portions of the infrared absorption cross-section for methanol (CH$_3$OH) as measured by frequency-stabilized cavity ring-down spectroscopy (FS-CRDS) at wavelengths near $λ$ = 2.0 $μ$m. High-resolution spectra of two gravimetric mixtures of CH$_3$OH-in-air with nominal mole fractions of 202.2 $μ$mol/mol and 45.89 $μ$mol/mol, respectively, were recorded at pressures between 0.8 kPa and 102 kPa and at a temperature of 298 K. Covering the experimental wavenumber range of 4990 cm$^{-1}$ to 5010 cm$^{-1}$ in increments of 0.0067 cm$^{-1}$ and with an instrument linewidth of 30 kHz, we observed an evolution in the CH$_3$OH spectrum from resolved absorption lines at a low pressure (0.833 kPa) to a pseudo-continuum of absorption at a near-atmospheric pressure (101.575 kPa). An analysis of resolvable features at the lowest recorded pressure yielded a minimum intramolecular vibrational energy redistribution (IVR) lifetime for the OH-stretch ($ν_1$) plus OH-bend ($ν_6$) combination of $τ_{IVR} \geq$ 232 ps - long compared to other methanol overtones and combinations. Consequently, we show that high-resolution FS-CRDS of this relatively weak CH$_3$OH combination band provided an additional avenue by which to study the intramolecular dynamics of this simplest organic molecule with hindered internal rotation.

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Hongming Yi, Adam J. Fleisher. 2019-11-24. High-resolution cavity ring-down spectroscopy of the $ν_1 + ν_6$ combination band of methanol at 2.0 $μ$m. https://doi.org/10.1063/1.5125146

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