DISCOVERY OF THE ELECTRONIC SPECTRA OF HPS AND DPS

Abstract

The hitherto unknown electronic spectrum of the closed shell transient molecule HPS has been observed in the 685 - 846 nm region by laser-induced fluorescence and single vibronic level emission techniques. HPS (and DPS) were produced in a pulsed electric discharge jet using a precursor mixture of 3\% PH$_3$ and 1\% H$_2$S (or PD$_3$ and D$_2$S) in high pressure argon. The weak set of observed bands are assigned to the $\~A $^1$A^{\prime \prime}-\~X $^1$A^{\prime}$ electronic transition on the basis of chemical evidence, isotope shifts and the correspondence of the vibrational frequencies, excitation energy, and band contours with predictions based on our own high level {\em ab initio} calculations. Theory predicts that the HPS bond angle decreases on electronic excitation, contrary to expectations based on Walsh diagrams.