Knowledge Bank

Infrared spectra of jet-cooled CH$3$OD and CH$3$OH in the CH stretch region are observed by coherence-converted population transfer Fourier transform microwave-infrared (CCPT-FTMW-IR) spectroscopy (E torsional species only) and by slit-jet single resonance spectroscopy (both A and E torsional species, CH$3$OH only). Previously, we reported$ \textbf{2010}, 114, 6818}$ the analysis of $\nu 3$ symmetric CH stretch region (2750$-$2900cm$^{-1}$),andthepresentworkextendstheanalysistohigherfrequency(2900$-$3020cm$^{-1}$).Theoverallobservedspectracontain17interactingvibrationalbandsforCH$_3$ODand28forCH$_3$OH.ThesignsandmagnitudesofthetorsionaltunnelingsplittingsarededucedforthreeCHfundamentals($\nu_3$, $\nu 9$, $\nu 2$) of both molecules and are compared to a model calculation and to ab initio theory. The number and distribution of observed vibrational bands indicate that the CH stretch bright states couple first to doorway states that are binary combinations of bending modes. In the parts of the spectrum where doorway states are present, the observed density of coupled states is comparable to the total density of vibrational states in the molecule, but where there are no doorway states, only the CH stretch fundamentals are observed. A time-dependent interpretation of the present FTMW-IR spectra indicates a fast ($\sim$ 200 fs) initial decay of the bright state followed by second, slower redistribution ($\sim$ 1$-$3 ps). The qualitative agreement of the present data with the time-dependent experiments of Iwaki and Dlott $ \textbf{2000}, 104, 9101}$ provides further support for the similarity of the fastest vibrational relaxation processes in the liquid and gas phases.