Samartzis Peter C, Hansen Nils, Wodtke Alec M
Department of Chemistry and Biochemistry, University of California Santa Barbara, Santa Barbara, CA 93106, USA.
Phys Chem Chem Phys. 2006 Jul 7;8(25):2958-63. doi: 10.1039/b603129c. Epub 2006 Apr 7.
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).
我们报告了通过速度成像测量的234 - 280 nm区域内ClN₃光解后的Cl((²P₃/₂))和Cl*((²P₁/₂))碎片图像。动能分布随光解波长而变化，从234和240 nm处的双峰形变为266和280 nm处的单峰形。在存在两个峰的情况下，Cl和Cl*碎片的峰比显著不同。266和280 nm处的单峰以及234和240 nm处较快的峰被归因于Cl + 线性-N₃解离通道，这与之前的工作一致。双峰分布中的慢峰被归因于N₃的高能形式（HEF）的形成。讨论了HEF-N₃的可能身份。将我们的数据与光碎片平移光谱结果相结合，我们确定了在4.83 ± 0.17 eV光解能量下HEF-N₃出现的阈值。这种阈值行为类似于最近报道的关于HN₃光解波长依赖性的结果，其中该阈值与S₁势能面上HN₃的闭环异构体相关。我们还注意到，在ClN₃中观察到的HEF-N₃形成阈值出现在产物可获得的能量等于从线性到环状-N₃的异构化势垒的地方。
