Knowledge Bank

Photoacoustic spectra of $CH4$ and $NH3$ in the three quanta region have been recorded using the first Stokes output of a Ti:sapphire laser Raman shifted by $H2$ or $D2$. The single-mode, narrow bandwidth radiation $(0.0150.02cm-1$, 3-4 nsec pulse), together with the highly sensitive photoacoustic detection, provide exceptional quality spectra. Double resonance is being used lo make new spectroscopic assignments in these overtone bands. A tunable diode laser operating at $1300cm-1$ is used to probe assigned transitions in the $v4$ fundamental while the Raman-shifted Ti:sapphire laser is scanned through the overtone band. The occurrence of a double resonance signal establishes the lower level rotational quantum numbers of the overtone transition.