Vibrational predissociation in the HCl dimer.

Area of Science:

• Physical Chemistry
• Molecular Spectroscopy
• Chemical Physics

Background:

• Vibrational predissociation is a key decay mechanism for van der Waals clusters.
• Understanding dissociation dynamics provides insights into intermolecular forces and energy transfer.
• The HCl dimer serves as a model system for studying hydrogen-bonded complexes.

Purpose of the Study:

• To combine theoretical calculations and experimental measurements to study the vibrational predissociation of the HCl dimer.
• To investigate the dynamics of excited states, including linewidths, product-state distributions, and excited-state alignment.
• To compare theoretical predictions with experimental observations and identify areas for improvement in theoretical models.

Main Methods:

• Theoretical calculations employed the Fermi golden rule approximation to compute photodissociation linewidths and product-state distributions.
• Quasibound states were used to calculate line strengths for transitions from the ground state to excited states.
• Experimentally, the photofragment angular distribution method was used to determine final-state distributions for monomer stretch excited states.

Main Results:

• Excited-state alignment of the HCl dimer is completely lost on the dissociation timescale, unlike the HF dimer.
• Reasonable agreement was found between theoretical and experimental results for product-state distributions and line strengths.
• Computed lifetimes were 1-2 orders of magnitude shorter than experimental values, suggesting deficiencies in the potential energy surface.

Conclusions:

• The study provides a comprehensive understanding of the vibrational predissociation dynamics of the HCl dimer.
• Discrepancies in computed lifetimes highlight the need for improved potential energy surfaces for accurate theoretical modeling.
• The loss of excited-state alignment offers crucial insights into the rapid dissociation processes in hydrogen-bonded dimers.