Dynamics Behind the Long-Lived Coherences of I2in Solid Xe.

The absorption spectrum of I2in solid Xe shows resolvedzero-phonon lines and phonon side bands near the origin of the B←Xtransition (550–625 nm). The long-lived |B⟩⟨X| coherence in this energy range(T2= 600 fs on average) emerges as vibrationallyunrelaxed fluorescence in resonance Raman (RR) spectra. Upon excitationin the structureless continuum at 532 nm, the oscillatory RR progressionexhibits electronic dephasing time of T2= 150 fs. Two RR progressions with markedly different vibrationalcoherence on the X-state are observed. The main progression of sharpovertones (T2> 21 ps) is assignedtomolecules trapped in double-substitution sites. The minor progression,which shows dephasing times T2= 6–0.6ps for v= 1–8, is assigned to molecules intriple-substitution sites. The line progressions allow a detailedcharacterization of the solvated B- and X-state potentials. Time-resolvedcoherent anti-Stokes Raman scattering is used to probe selected vibrationalcoherences on the X-state. Assignments are obtained through moleculardynamics simulations, which reproduce the relative dephasing ratesbetween the two sites, clarify the role of rotation-translation dynamics,and enable quantum dynamics simulations of the spectra by the potentialsof mean force that accurately describe the molecule–surroundinginteractions. [ABSTRACT FROM AUTHOR]