ISOMERIZATION AND COLLISIONAL DEACTIVATION OF HIGHLY VIBRATIONALLY EXCITED AZULENE MOLECULES AFTER UV EXCITATION AT 248 AND 193 NM

Highly vibrationally excited azulene molecules in the electronic ground state were prepared by light absorption at 248 and 193 nm followed by internal conversion. Under collision-free conditions these molecules will isomerize to naphthalene. For azulene molecules excited with 193 nm (E = 52 800 cm-1), a specific rate constant of k(E) = (4.0 +/- 0.5) X 10(5) s-1 was determined. Isomerization of azulene excited with 248 nm (E = 41 300 cm-1) could not be observed under our experimental conditions. Collisional energy transfer from excited azulene to He, Ar, N2, C3H8, n-C8H18, and n-C8F18 was also investigated by using time-resolved UV absorption spectroscopy. Absolute values of the average energy transferred per collision <DELTA-E> were in close agreement with results from previous studies. For large polyatomic colliders like n-C8H18 and n-C8F18, <DELTA-E> values were found to be proportional to the average internal energy <E> of the excited azulene molecule. However, for the small colliders He and Ar, only at energies up to about 15 000 cm-1 does (<DELTA-E>) increase proportionally with <E>, while at higher energies the energy dependence of (<DELTA-E>) becomes weaker. N2 and C3H8 represent intermediate cases.