High-resolution VUV photoionization spectroscopy of HD between the X 2Σ +gv+ = 0 and v+ = 1 thresholds

Abstract

The photoionization spectrum of HD has been recorded in the region of the first vibrationally excited level (v⁺ = 1) of the X ²Σ⁺_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 v⁺ = 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 (v⁺ > 1) of HD⁺ have also been observed and their interaction with the v⁺ = 1 channel is discussed.