Vibrational frequencies of the 2p 2A2″ and 3d 2E″ states of the triatomic deuterium molecule

We investigated the vibrational energies in the ${\text{2p\hspace{0.17em}}}^2{A}_2^{″}$ and ${\text{3d\hspace{0.17em}}}^2{E}^{″}$ states of the triatomic deuterium molecule ${\mathrm{D}}_3$ . The experiments were performed using a fast neutral beam photoionization spectrometer recently developed at Freiburg. A depletion type optical double-resonance scheme using two pulsed dye lasers was applied. The measured vibrational frequencies of the ${\text{2p\hspace{0.17em}}}^2{A}_2^{″}$ state of ${\mathrm{D}}_3$ are compared to those of ${\mathrm{H}}_3$ and to theoretical values calculated from an ab initio potential energy surface. The data give insight into the importance of the coupling between the valence electron and the ion core.