PREDISSOCIATION OF THE NH/ND(C1-PI,V',J') STATES

The predissociation of the electronically excited NH/ND (c (1)PI) state was studied by accurate lifetime measurements. The pulsed generation of single rotational states of different vibrational levels was performed by dye laser excitation in the NH/ND c (1)PI-a (1)DELTA band system. The lifetime of ND(c,upsilon' = 0,J' = 1) is 500 +/- 10 ns. This value is close to the purely radiative lifetime of the rotationless state. The lifetime increases steadily up to J' = 15. The lifetime of ND(c,upsilon' = 1) is 235 ns for very low J' and decreases for higher J'. These shorter lifetimes are due to predissociation by the repulsive 1 (5)SIGMA- state. Similarly, the NH(c,upsilon' = 0) state is predissociated for all J', having an average lifetime of 463 ns for J' = 1-7. For J' > 7, the lifetime decreases steadily. The lifetime of NH(c,upsilon' = 1) is dominated by predissociation, with values near 65 ns for J' = 1-6. These experimental results are found to be in very good agreement with an ab initio electronic structure calculation of the radiative and predissociative decay rates.