Photodissociation of ClN3 at 157 nm: Theory suggests a pathway leading to cyclic N-3

摘要

The photodissociation dynamics of chlorine azide (ClN3) at the 157 nm region was studied theoretically using the multireference configuration interaction method and the complete active space self-consistent field direct dynamics method. The excitation at the 157 nm region was assigned to the 4 (1)A(')(S-7)<- X (1)A(')(S-0) transition. A likely pathway for the formation of cyclic N-3 after this transition was identified by direct dynamics as follows: ClN3 excited to 4 (1)A(')(S-7) dissociates after about 40 fs to excited N-3(2 (2)A('), with about 44 kcal/mol internal energy) +Cl(P-2). This vibrationally hot N-3(2 (2)A(')) goes diabatically through a conical intersection with N-3(1 (2)A(')) at 44 fs onto 1 (2)A('). At 19 fs later and repeatedly after every 55 fs, N-3(1 (2)A(')) crosses and trickles down via Coriolis coupling to N-3(2 (2)A(')/ B-2(1)) state, which has a potential minimum at the cyclic-N-3 structure. Some fraction of N-3(2 (2)A(')/ B-2(1)) produced will survive dissociation and will be found as the cyclic N-3, and some other fraction will eventually dissociate to N(D-2)+N-2 over a high barrier found previously.