Dynamics behind the long-lived coherences of I2 in solid Xe

Area of Science:

• Physical Chemistry
• Spectroscopy
• Condensed Matter Physics

Background:

• The B←X transition of I2 in solid xenon exhibits complex spectral features, including zero-phonon lines and phonon side bands.
• Understanding molecular coherence and dephasing dynamics in solid matrices is crucial for characterizing solute-solvent interactions.

Purpose of the Study:

• To investigate the vibrational coherence and electronic dephasing times of I2 in solid xenon.
• To characterize the solvated B- and X-state potentials of I2 by analyzing resonance Raman spectra.
• To elucidate the role of molecular site occupancy and dynamics in spectral properties.

Main Methods:

• Resonance Raman (RR) spectroscopy was employed to observe vibrational coherences.
• Time-resolved coherent anti-Stokes Raman scattering (TR-CARS) was used to probe vibrational coherences on the X-state.
• Molecular dynamics (MD) simulations were performed to assign spectral features and understand site-specific dynamics.

Main Results:

• Two distinct RR progressions were observed, attributed to I2 molecules in double-substitution (sharp overtones, T2 > 21 ps) and triple-substitution (T2 = 6-0.6 ps) sites.
• Vibrationally unrelaxed fluorescence in RR spectra indicates long-lived |B⟩⟨X| coherence (T2 = 600 fs).
• Electronic dephasing time (T2) of 150 fs was measured upon excitation in the continuum.
• MD simulations accurately reproduced relative dephasing rates and clarified the role of rotation-translation dynamics.

Conclusions:

• The study successfully characterized the solvated B- and X-state potentials of I2 in solid xenon.
• Distinct vibrational coherence dynamics were observed for I2 in different substitutional sites.
• Molecular dynamics simulations provide a powerful tool for interpreting complex spectroscopic data in condensed phases.