Knowledge Bank

Spectra of the 2$\nu 4$ overtone of methane, measured at $100\circ K$ and room temperature, were analyzed using the third-order theory of $Fox1$ for scalar perturbations and the formalism of Moret-$Bailly,2$ with appropriate modifications, for tensor perturbations and resultant tetrahedral fine-structure splittings. Theory and experiment were in qualitatively good agreement from 2520 to 2610 $cm-1$. New values for excited-state molecular constants were determined. From measured line intensities, a band intensity of (7.50 $\pm$ 0.97) $\times$ 10$\mathrm{<mrow\; data-mjx-texclass="ORD">-20</mrow>}$ $cm-1$ (molec. $cm-2$)$\mathrm{<mrow\; data-mjx-texclass="ORD">-1</mrow>}$ at STP was theoretically projected. Transition dipole moments were evaluated, and their quantum-number dependence was investigated.