Sequential two photon excitation of the C2 Swan transitions and C2 relaxation dynamics in rare gas solids

Abstract

The C₂ d ³Π_g–a ³Π_u emission in solid Ar and Ne is excited both by sequential absorption of two identical photons and by two unlike photons using two separately tunable lasers. It is shown that excitation of guest molecules by sequential absorption should be a useful technique for populating levels unaccessible in a single step absorption process. The different phonon band shapes observed for the X ¹Σ_g⁺–A ¹Π_u and d ³Π_g–a ³Π_u transitions are interpreted in terms of the electronic structure of the states involved. The vibrational relaxation in the d ³Π_g state is fast and shows erratic variation with v. The lifetimes of the low a ³Π_u levels vary from 65 μs for v=0 to less than 0.5 μs for v=3. The rate of the spin and symmetry forbidden radiationless crossing into the ground state shows a strong temperature dependence expected by theory. The efficient two photon excitation of the low d ³Π_g levels leads to population inversion and stimulated emission on the d ³Π_g→a ³Π_u Swan bands.