Laser Spectroscopy of the H 2 ( n = 3 Triplet Gerade) Complex: Fine Structure of the Levels in para-H 2

Abstract

Doppler-free LIF spectroscopy was performed on a beam of para-H 2 (95% enriched) in the metastable c 3Π − u state. Using the method of beam saturation spectroscopy, the resolution was increased to 20 MHz FWHM. Compared to the preceding paper of this series, this allowed the fine structure of the H 2( n = 3) states to be largely resolved. The total number of independently measured fine structure splittings in the levels v = 0 to 3 was 66. Theoretically the fine structure in the n = 3 compared is described by 17 coupling constants. The present study has provided for the first time a sufficient number of independent fs measurements to allow, in principle, an unambiguous determination of all 17 constants. The eigenvectors of the true, mixed wavefunctions as obtained in the preceding paper were here used as a critical prerequisite to the diagonalization of the fs Hamiltonian. In practice, in the fitting routine some of the nondiagonal constants were found to be highly statistically correlated within the experimental error. These constants have only collective significance. This is a fundamental limitation, because the experimental resolution was already close to the natural linewidth limit. The variation of the leading diagonal constants with v and, comparing with other work, with n is discussed.