Laser Spectroscopy of the H 2 ( n = 3 Triplet Gerade) Complex: Vibrational and Rotational Coupling between the Electronic States

• Published in: Journal of molecular spectroscopy Vol. 163; no. 2; pp. 381 - 397
• Main Authors: Jozefowski, L., Ottinger, C., Rox, T.
• Format: Journal Article
• Language: English
• Published: Elsevier Inc 01.02.1994
• ISSN: 0022-2852; 1096-083X
• DOI: 10.1006/jmsp.1994.1034

A beam of H 2 molecules in the metastable c 3Π − u state has been generated using a specially designed electron impact excitation source. Crossing this beam at right angles with the beam from a CW single-mode ring dye laser, laser-induced fluorescence spectra are recorded from the excitation of the H 2( n = 3) h 3Σ + g, g 3Σ + g, i 3Π ± g and j 3Δ ± g states with subsequent VUV emission to the b 3Σ + u state. One hundred lines were measured with a resolution of 100-150 MHz FWHM. They originate from the c-state levels with v = 0-3 and N = 0-4. Absolute wavenumbers of these transitions were determined with an accuracy of 2-6 × 10 −3 cm −1 i.e.. similar to the resolution. This is an improvement by one order of magnitude compared to the well-known data by H. M. Crosswhite ("The Hydrogen Wavelength Tables of Gerhard Heinrich Dieke," Wiley-Interscience. New York. 1972). Spacings between the fine structure centroids of different rotational lines were measured to within 10 MHz. On the basis of this large amount of data. a new analysis of the mixing between the four n = 3 states was undertaken. The 15 molecular constants appearing in the rotational/orbital matrix elements were adjusted to give an optimum simultaneous fit of the experimental term energies with those calculated by matrix diagonalization. The eigenvectors obtained from the diagonalization give a clear quantitative picture of the v- and n-dependent mixing between the four basis states. For example, the i 3Π ± g/ j 3Δ ± g coupling increases strongly from N = 1 to 4 in v = 0, but much less so in v = 3. For the four states of "+" symmetry, the energy separation between the respective vibrational levels has a profound effect on the coupling.