High-resolution VUV photoionization spectroscopy of HD between the X 2Σg+ ν+=0 and ν+=1 thresholds

The photoionization spectrum of HD has been recorded in the region of the first vibrationally excited level (nu(+) = 1) of the X (2)Sigma(g)(+) ground state of the HD+ ion using a narrow bandwidth vacuum ultraviolet (VUV) laser. Spectral positions, intensities and line widths are reported for all resonances observed between 126 100 and 126 700 cm(-1). The np Rydberg series converging to the nu(+) = 1, N+ = 0 and 2 states of the ion have been observed up to n = 150 and used to determine the corresponding ionization thresholds in a multichannel quantum defect theory analysis. After subtraction of the ionic vibrational energy the adiabatic ionization energy of HD was determined to be 124 568.491 +/- 0.017 cm(-1). Several low n interloper Rydberg states converging to higher vibrational levels (nu(+) > 1) of HD+ have also been observed and their interaction with the nu(+) = 1 channel is discussed.