Study of triplet states by equal-frequency two-photon transitions in Na2

The experiments were arranged with a pulsed dye laser and a cross oven. A double-pen chart recorder simultaneously traced the two-photon excitation spectra monitored by two photomultipliers with interference filters centered at 3600 and 4300 Å, respectively. The observed two-photon transitions with a linewidth of ~0.2 Å were distributed discretely and nonuniformly and were close to the calculated values for searching the intermediate singlet-triplet mixing levels in Na2. This means that the observed signals were individually enhanced by a near-resonant mixing level. While most of the corresponding recorded lines in the two traces had coincident wavelength locations and comparable intensities, a part of the lines at the longer wavelength sides of the traces with moderate or weaker intensities appeared alternately. The upper states for the lines which only appeared in the 4300 Å trace or in both of the traces were assumed to be (2)3Π g and a higher (n)3Λ g state, respectively. Temperature and total pressure was varied. Finally, the laser beam was split into two with combined polarization situations. These aided the identification of the two- photon transitions.