  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 $\lambda$ = 2.0 $\mu$m.
High-resolution spectra of two gravimetric mixtures of CH$_3$OH-in-air with
nominal mole fractions of 202.2 $\mu$mol/mol and 45.89 $\mu$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 ($\nu_1$) plus OH-bend ($\nu_6$) combination of $\tau_{IVR} \geq$
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.
