Observation of the v=20-17 band of HD+, experimental evidence for an asymmetric electron distribution

The v=20-17 band of the HD+ molecular ion hs been observed using a sequential two-photon photodissociation technique. The experiments were performed by Doppler - tuning a fast beam of HD+ into resonance with the fixed frequency of a collinear carbon dioxide laser beam. Doppler limited linewidths of about 5 MHz were achieved, permitting the partial resolution of the hyperfine structure. The two lowest dissociation limits of HD+, H+ + D(ls) and H(ls) + D+, are separated by about 30 cm-1, the former being the lower limit. For very high vibrational levels, such as v=20 which lies about 100 cm-1 below the H+ + D(ls) limit, the electron density about the deuteron is expected to be higher than about the proton. This suggestion is confirmed by simulations of the hyperfine structure for transitions of the 20-17 band