Line-shape studies in high-resolution stimulated resonance Raman spectroscopy and application to accurate determinations of hyperfine splittings in I-2

We studied stimulated resonance Raman transitions between hyperfine sublevels of the ground electronic state X(1) Sigma(0+g)(v = 0, J = 13) of I-2. Resonances narrower than 10 kHz (HWHM) were obtained. A detailed theoretical and experimental analysis of the line shape is presented. The pressure broadening of Raman resonances was found to be 7 +/- 1 kHz/mTorr. The role of the beam divergence was investigated and shown to yield only a small broadening but some asymmetry of the lines. In the transit-time limit the theory predicts that the slow molecules should play a dominant role, as in saturation spectroscopy. Our experimental conditions are very close to that regime, and we discuss the improvements that should be made in order to reach it in future experiments. Finally, six hyperfine splittings of the ground state of I-2 were determined with a 0.2-kHz accuracy. (C) 1996 Optical Society of America.