A vector correlation study using a hexapole-oriented molecular beam: photodissociation dynamics of oriented...

Area of Science:

• Chemical Physics
• Molecular Dynamics
• Photochemistry

Background:

• Understanding photodissociation dynamics is crucial for chemical reaction mechanisms.
• Isohaloethane (1-bromo-2-chloro-1,1,2-trifluoroethane) serves as a model system for studying halogenated compound photochemistry.

Purpose of the Study:

• Investigate the photodissociation pathways of isohaloethane at 234 nm.
• Determine the speed and angular distributions of bromine (Br) and chlorine (Cl) atom fragments.
• Analyze the vector correlation between molecular orientation and fragment recoil to elucidate dissociation dynamics.

Main Methods:

• Utilized a sliced imaging technique with an oriented molecular beam.
• Performed spin-orbit selection of Br and Cl atoms.
• Analyzed fragment speed and angular distributions, and determined the anisotropic parameter (β).

Main Results:

• Bromine atom formation (Br and Br*) showed anisotropic angular distributions and Gaussian-like speed distributions, indicating direct dissociation.
• Chlorine atom fragments exhibited isotropic angular distributions and Boltzmann-like speed distributions, suggesting longer-lived parent molecules.
• The branching ratio favored Br atom formation (approx. 1.2), and vector correlation revealed a common excited state for fragment formation.

Conclusions:

• Bromine atom release occurs through direct excitation of nσ*(C-Br) states.
• Chlorine atom formation may involve indirect pathways through longer-lived intermediates.
• The combined oriented molecular beam and imaging technique is effective for determining transition dipole moments in photodissociation.