Riedle, Eberhard and Neusser, H. J. and Schlag, E. W.
Sub-Doppler Spectroscopy of Benzene in the "Channel-three" Region.
In: Faraday Discussions of the Chemical Society, Vol. 75: pp. 387-394
In addition to an increased accuracy in the determination of structural parameters sub-
Doppler spectroscopy of large molecules is shown to render valuable information about intramolecular
processes and relaxation mechanisms. As an example we have measured the
Doppler-free rotationally resolved two-photon spectrum of two vibronic bands of CsHs,
1461; and 14i1;. Compared with the 14i1: band (EcxE :,:=css 2492 cm-') a drastically reduced
number of sharp lines is observed in the 14i1; band (Eence=ss 3 412 cm-I). The X = 0
rotational lines are still seen, while K # 0 lines disappear. This can be understood in terms
of Coriolis coupling between the 14'1' state and other vibrational states within S1 and a
subsequent om-radiative process. This coupling might be the explanation for the drastic
onset of line broadening in C6H6 at an excess energy of 3000 cm-', " channel three." The
line broadening is then due to a different process from that responsible for the population
lifetime of s1.