Knowledge Bank

Coherence-converted population transfer microwave-infrared double resonance spectroscopy is employed to record the rotationally state-selected infrared spectra of jet-cooled CH$3$OD in the C-H stretch region (2750$-$3020cm$^{-1}$).TheobservedinfraredspectraresultfromtheE-speciesmicrowavetransitions(1$_0$ \leftarrow 1$\mathrm{<mrow\; data-mjx-texclass="ORD">-1</mrow>}$ at 18.957 GHz, 2$0$ \leftarrow 2$\mathrm{<mrow\; data-mjx-texclass="ORD">-1</mrow>}$ at 18.991 GHz, and 3$0$ \leftarrow 3$\mathrm{<mrow\; data-mjx-texclass="ORD">-1</mrow>}$ at 19.005 GHz). The present spectra of CH$3$OD contain 17 interacting vibrational bands ($J\prime$ = 0). In additional to the three C-H stretch fundamentals ($\nu 3$:2841.7 cm$\mathrm{<mrow\; data-mjx-texclass="ORD">-1</mrow>}$, $\nu 9:2954.4cm$^{-1}$ and $\nu 2:2998.9cm$^{-1}$),14additionalbandoriginsarefoundintheregionofthebinarycombinationsoftheCHbends(2890$-$2950cm$^{-1}$). Although the A-species was inaccessible in the present work, the pattern of E-species reduced energies suggests that the torsional tunneling splittings of $\nu 3$ and $\nu 9$ are normal, whereas $\nu 2$ is inverted. The number and distribution of the observed vibrational bands support a stepwise coupling scheme in which the CH stretch bright state couples first to the binary C-H bend combinations, and then to all of the higher order vibrational combinations. A time-dependent interpretation in the asymmetric region indicates a fast (170 fs) initial decay of the bright state.