Knowledge Bank

The $A~2A1-X~2B1$ electronic band system of the AsD$2$ and AsHD free radicals has been observed by laser induced fluorescence (LIF) spectroscopy. AsD$2$ (or AsHD) was produced in a pulsed supersonic expansion by electric discharge dissociation of a mixture of 5% AsD$3$ (or AsHD mixture) seeded in argon. Single vibronic level emission spectra have been obtained for both AsD$2$ and AsHD. The observed LIF transitions of AsD$2$ in the 411 - 505 nm region exhibit a long progression in the excited state bending vibration. High-resolution rotationally resolved spectra of the $000$ band of AsD$2$ were also recorded. This $\backslash italicc$-type band shows prominent $\Delta Ka=\pm 3$ transitions due to the large change in the asymmetry parameter upon electronic excitation. Extensive hyperfine splittings were resolved which allowed the determination of the excited state Fermi contact parameter. The data have been used to refine the molecular structure of the AsH$2$ radical.