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

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 2A’1 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. [ABSTRACT FROM AUTHOR]