Abstract

H₃ is the simplest of all neutral triatomics and, therefore, of significant fundamental interest. We exploit the metastability of the rotationless levels of the $2p{A}_2^{"}$ state to perform laser spectroscopy on a fast neutral beam of H₃.¹ In particular, a two-step photoionization scheme has been used to measure the positions of vibrationally excited levels of the n= 3 Rydberg manifold of H₃. We find symmetric-stretch vibrational frequencies of 3315 and 3168 cm⁻¹ for the $3s^2{A}_1^{\text{'}}$ ,and 3d²E″states, respectively; these lie close to the calculated frequency of 3189 cm⁻¹ for the ion.² Overtone frequencies of the 3p ²E′state are determined as well.

© 1988 Optical Society of America