PHOTOFRAGMENT ACTION SPECTROSCOPY OF THE ACETYLENE MOLECULE IN THE VACUUM-ULTRAVIOLET

The photodissociation dynamics of acetylene to hydrogen atoms, C2H2 -- > C2H + H and C2D2 --> C2D + D, with C2H and C2D in the ground <(X)ove r tilde (2) Sigma(+)> and/or excited electronic <(A)over tilde (2) Pi> states, has been investigated for the first time with tunable narrow- band vacuum ultraviolet laser radiation between 121 and 133 nm by empl oying hydrogen atom photofragment action spectroscopy. Action spectra have been taken at 2.5 cm(-1) resolution with acetylene in a molecular beam adiabatically cooled internally to about 4 K. They exhibit prono unced discrete predissociative resonances of Rydberg and valence excit ed states resolved to homogeneous widths. From them dissociation lifet imes of individual states from 5 x 10(-14) s to longer than 2 x 10(-12 ) s are derived.