Dynamics of Cl (P-2(j)) Atom Formation in the Photodissociation of Fumaryl Chloride (ClCO - CH = CH - COCl) at 235 nm: A Resonance Enhanced Multiphoton Ionization (REMPI) Time-of-Flight (TOF) Study

作者：Kawade Monali; Saha Ankur; Upadhyaya Hari P^*; Kumar Awadhesh; Naik Prakash D; Bajaj P N

来源：Journal of Physical Chemistry A, 2011, 115(9): 1538-1546.

DOI：10.1021/jp1100279

The photodissociation dynamics of fumaryl chloride (ClCO-CH=CH-COCl) has been studied in a supersonic molecular beam around 235 nm using resonance enhanced multiphoton ionization (REMPI) time-of-flight (TOF) technique by detecting the nascent state of the primary chlorine atom. A single laser has been used for excitation of fumaryl chloride and the REMPI detection of chlorine atoms in their spin-orbit states, Cl (P-2(3/2)) and Cl* (P-2(1/2)). We have determined the translational energy distribution, the recoil anisotropy parameter, beta, and the spin-orbit branching ratio for chlorine atom elimination channels. To obtain these, measured polarization-dependent and state-specific TOF profiles are converted into kinetic energy distributions, using a least-squares fitting method, taking into account the fragment recoil anisotropies, beta(i). The TOF profiles for both Cl and Cl* are found to be independent of laser polarization; i.e., beta is well characterized by a value of 0.0, within the experimental uncertainties. Two components, namely, the fast and the slow, are observed in the translational energy distribution, P(E-T), of Cl and Cl* atoms, and assigned to be formed from different potential energy surfaces. The average translational energies for the fast components of the Cl and Cl* channels are 14.9 +/- 1.6 and 16.8 +/- 1.6 kcal/mol, respectively. Similarly, for the slow components, the average translational energies of the Cl and Cl* channels are 3.4 +/- 0.8 and 3.1 +/- 0.8 kcal/mol, respectively. The energy partitioning into the translational modes is interpreted with the help of various models, such as impulsive and statistical models. Apart from the chlorine atom elimination channel, molecular hydrogen chloride (HCl) elimination is also observed in the photodissociation process. The HCl product has been detected, using a REMPI scheme in the region of 236-237 nm. The observation of the molecular Ha in the dissociation process highlights the importance of the relaxation process, in which the initially excited parent molecule relaxes to the ground state from where the molecular (HCl) elimination takes place.

• 出版日期2011-3-10