Fine structure of the H2 5g–4f inter-Rydberg transition revealed by difference frequency laser spectroscopy

• Published in: The Journal of chemical physics 2000-12, Vol.113 (22), p.10143-10153
• Main Authors: Uy, D., Gabrys, C. M., Oka, T., Cotterell, B. J., Stickland, R. J., Jungen, Ch, Wüest, A.
• Format: Article
• Language: English
• ISSN: 0021-9606; 1089-7690
• DOI: 10.1063/1.1322634

The spectrum of the 5g–4f inter-Rydberg band of H2 has been recorded with a difference frequency laser system and analyzed using multichannel quantum defect theory (MQDT). New transitions have been observed; in addition to the singlet–triplet splittings previously observed, the hyperfine structure of the ortho-hydrogen spectrum is partially resolved in the present experiment. MQDT is used to analyze the data in a two stage process. First, the ab initio MQDT predictions were refined by fitting the quantum defect functions over a range of internuclear separation R. Second, 4f singlet and triplet quantum defects are extracted from the para-hydrogen spectra, i.e., those lines without complicating hyperfine structure. This information was then used to calculate the fine structure of a sample ortho-hydrogen line, R3(2)v+=0. While the spectra are predominantly composed of absorption lines, some transitions from high vibrational levels of the 5g triplet manifold to 4f triplet levels are observed in stimulated emission.