Measurement of vibrational frequencies of the H3 molecule using two-step photoionization

Abstract
A two‐step photoionization scheme is used to determine vibrational frequencies of the n=3 Rydberg states of triatomic hydrogen. Symmetric‐stretch frequencies in orthotrihydrogen of 3212.1 and 3168 cm−1 are measured for the N=1 levels of the states 3s 2A1 and 3d 2E‘, respectively. Transitions to bending‐mode excited levels in the 3d states and overtone levels of the 3p 2 E’ state are observed also.