Dynamics of Cl (²P_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

Abstract

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 ((2)P(3/2)) and Cl* ((2)P(1/2)). We have determined the translational energy distribution, the recoil anisotropy parameter, β, 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, β(i). The TOF profiles for both Cl and Cl* are found to be independent of laser polarization; i.e., β 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 HCl 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.

Photodissociation of Benzoyl Chloride: A Velocity Map Imaging Study Using VUV Detection of Chlorine Atoms

“…In α,β-unsaturated alkyl chlorides, multiple C–Cl bond dissociation pathways along with HCl formation are experimentally observed. − For acyl chlorides like CH 3 COCl, the C–Cl bond cleaves preferentially over the C–C bond with fast dissociation via an exit barrier that results from surface crossing between electronic states, in contrast to the usual intersystem crossing mechanism seen in Norrish type-I reaction of aliphatic aldehydes and ketones. − Enones like acryloyl chloride (CH 2 CHCOCl) show two different Cl fragmentation channels along with HCl formation and CO elimination. − In these two channels, the fast Cl with high translational energy results from an electronic predissociation, and the low-energy channel mainly appears from excited vibrational states of S 0 following IC. Fumaryl chloride (Cl–CO–CHCH–CO–Cl) supposedly also shows a similar behavior …”

Ground‐state dissociation pathways for the molecular cation of 2‐chlorothiophene: A time‐of‐flight mass spectrometry and computational study

“…The laser‐based ionization experimental setup with a supersonic molecular beam (MB) facility equipped with a time‐of‐flight (TOF) mass spectrometer has been described in previous publications . Briefly, it consists of an expansion chamber, ionization chamber and a flight tube.…”

“…The laser-based ionization experimental setup with a supersonic molecular beam (MB) facility equipped with a time-of-flight (TOF) mass spectrometer has been described in previous publications. [35][36][37][38] Briefly, it consists of an expansion chamber, ionization chamber and a flight tube. A pulsed supersonic molecular beam was generated using a solenoid valve, with a 0.8 mm nozzle and 500 μs opening time.…”

Dissociation pathways for the molecular cation of 3,4‐dichloro‐1,2,5‐thiadiazole: A time‐of‐flight mass spectrometry and computational study

“…The laser‐based ionization experimental setup with a supersonic molecular beam (MB) facility equipped with a time‐of‐flight (TOF) mass spectrometer has been described in detail elsewhere . Briefly, it consists of an expansion chamber, ionization chamber and a flight tube.…”

“…The laser-based ionization experimental setup with a supersonic molecular beam (MB) facility equipped with a time-of-flight (TOF) mass spectrometer has been described in detail elsewhere. [19][20][21] Briefly, it consists of an expansion chamber, ionization chamber and a flight tube. The system was differentially pumped, using two similar 9-inch turbomolecular pumps (TMP), backed by rotary pumps.…”