👤 Peter C Samartzis

We report the first time-resolved study of the photochemistry of chlorine azide (ClN3) by femtosecond velocity-map imaging (fs-VMI). The dissociation dynamics are initiated at 4.6 eV and the photofragments are detected by multiphoton ionization using an intense laser field centered at 803 nm. A dissociation time of 262 ± 38 fs was measured from the rising time of the co-fragments N3 and Cl. The time dependency of the angular distribution of N3, which converges from β2 ~ 2 to β2 = 1.61 ± 0.07 in 170 ± 45 fs, reveals the parallel nature of the transition dipole moment. Show less

We report evidence that cyclic-N(3) is exclusively produced in the 157-nm photolysis of ClN(3). Photoproduct translational energy measurements reveal a single-peaked distribution for an N(3)-formation channel with maximum and minimum translational energies matching the theoretically predicted minimum and maximum binding energies of cyclic-N(3), respectively. The absence of linear-N(3) greatly simplifies the data analysis. The zero-Kelvin heat of formation of cyclic-N(3) is derived experimentally (142+/-3.5 kcal/mol) and is in excellent agreement with the best existing determinations from other studies. Show less

We report Cl((2)P(3/2)) and Cl*((2)P(1/2)) fragment images following ClN(3) photolysis in the 234-280 nm region measured by velocity map imaging. Kinetic energy distributions change shape with photolysis wavelength from bimodal at 234 and 240 nm to single peak at 266 and 280 nm. Where two peaks exist, their ratio is significantly different for Cl and Cl* fragments. The single peak of 266 and 280 nm and the faster peak at 234 and 240 nm are assigned to a Cl + linear-N(3) dissociation channel, in agreement with previous work. The slow peak in the bimodal distributions is assigned to the formation of a high energy form (HEF) of N(3). Candidates for the identity of HEF-N(3) are discussed. Combining our data with photofragmentation translational spectroscopy results, we determined the threshold for the appearance of HEF-N(3) at 4.83 +/- 0.17 eV photolysis energy. This threshold behavior is similar to recently reported results on the wavelength dependence of HN(3) photolysis, where the threshold was associated with a ring closed isomer of HN(3) on the S(1) potential energy surface. We also note that the HEF-N(3) formation threshold observed for ClN(3) occurs where the energy available to the products equals the isomerization barrier from linear to cyclic-N(3). Show less

We present results of near-threshold photoionization of N3 photofragments produced by laser photodissociation of ClN3 at 248 nm. The time of flight of recoiling N3 is used to resolve two photochemical channels producing N3, which exhibit different translational energy release. The two forms of N3 resolved in this way exhibit different photoionization thresholds, consistent with their assignment to linear (X 2pi(g)) and cyclic N3. This result agrees with the existing theoretical calculations of excited and ionic states of N3 and strengthens previous experimental results which suggested that the ClN3 photolysis produces a cyclic form of N3. Show less