ACETYLENE FLUORESCENCE

Previously unobserved acetylene 1Au(1Σu-) → 1Σg+ fluorescence occurs following 1933-Å ArF laser excitation of C2H2 or C2H4 and their deuterated analogs in solid Ne and Ar hosts at 4.2 K. Acetylene is a photolysis product of matrix-isolated ethylene. Ground-state vibrational levels as high as ν″3 = 30 of the degenerate ν3 bending vibration are observed for C2D2. Only ν3 is appreciably active in the fluorescence. The negative ν3 anharmonicity, previously observed in the gas phase, also occurs in Ne host. Consideration of rotational selection rules indicates that the Ne host strongly hinders free rotation about the low-moment-of-inertia a ̂ axis in the excited state. © 1979.