Knowledge Bank

The predissociated $B~\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}A1\prime$ state of $CH3$ has a sub-picosecond $lifetime,a$ which causes all absorption bands in the $B~\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}A1\prime \leftarrow X~\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}A2″$ system to be unstructured, and molecular constants for the $B~$ state must be inferred from analysis of partly resolved lines in the corresponding bands of $CD3.b$ We observe isolated rotational transitions in the $B~\leftarrow X~$ origin band of $CH3$ using two-color resonant four-wave mixing (TC-RFWM) spectroscopy with an IR laser that excites known lines in the $\nu 3$ fundamental $bandc$ to label specific N, K levels of the $X~$ state. Analysis of TC-RFWM spectra involves fitting complex Lorentzian lineshapes and yields an updated value of $46,241\pm 5cm-1$ for $T0$ of the $B~$ state.