ELECTRONIC SPECTROSCOPY OF THE HYDROGEN MOLECULAR ION, $D^{+}_{2}$.

$^{1}$ A. Carrington, I.R. McNab and C.A. Montgomgrie, Phys. Rev. Lett. 61. 1573 (1988).Author Institution: Department of Chemistry, Southampton UniversityA description of the first measurements of an electronic spectrum of $D^{+}_{2}$ is presented. The lower states involved are the rotational levels of the high-lying vibrational state, $v=21$ of the $1s\sigma_{g}$ ground state, and the upper states are the vibration-rotation levels of the $2p\sigma_{u}$ long-range van der Waals state. Transitions between these levels are induced by Doppler tuning an ion beam of $D^{+}_{2}$ into resonance with an infrared laser. Excitation is detected by electric field dissociation of the upper levels, the resulting $D^{+}$ fragments being separated from other ions with a magnetic analyser, and detected with an electron multiplier. Theoretical calculations predict that the $2p\sigma_{u}$ long-range minimum, arising from the charge/induced-dipole interaction, supports seven vibration-rotation levels. We have detected transitions to all of them, and determined the vibrational and rotational constants which characterise the van der Waals state. A preliminary observation of this spectrum has been $reported^{1}$