Knowledge Bank

Although the vibration-rotation spectra of $H2S$ and $D2S$ have been the object of extensive study, the assignment of the $v3$ mode has never been observed in the gas phase. The matrix spectra reported here are analyzed in terms of the uncoupled oscillator approximation. This approach offers several advantages: 1) A separate eigenvalue equation can be written for each vibrational frequency. 2) Simple, geometry-independent, expressions relate the force constants to the isotopic shifts. 3) The frequency shift caused by the matrix cancels from the force constant calculation. 4) The neglect of anharmonicity is easy to assess.