Pulsed Doppler-free two-photon spectroscopy of polyatomic molecules

Doppler-free two-photon electronic spectra of a large polyatomic
molecule are recorded for the first time with pulsed laser
radiation of near Fourier-transform limited bandwidth (Δvnot, vert,
similar100 MHz). The resolution obtained is sufficient to resolve
individual rotational lines. Due to the high density of these
rotational transitions a strong Doppler-broadened background is
observed, which is, however, subtantially reduced by suitable
choice of photon polarizations. Different vibronic bands of benzene
(C6H6) are investigated and very accurate rotational constants are
found.