Time resolved coherent anti-Stokes Raman scattering of I-2 isolated in matrix argon: Vibrational dynamics on the ground electronic state

Time-resolved, electronically resonant, coherent anti-Stokes Raman scatteri ng is used to prepare and interrogate vibronic coherences of molecular iodi ne in matrix Ar. Coherences that involve evolution on the excited B((3)Pi ( 0u)) state, first- and third-order coherences, decay in less than one vibra tional period (tau < 300 fs). In contrast, as many as 200 vibrational perio ds of motion can be observed for Raman-prepared wave packets consisting of zero-phonon vibrational superpositions on the ground electronic state (seco nd-order coherence). Packets consisting of v=4, 5 and v=3, 4, 5 on the X((1 )Sigma (g)) state decay with a half-life of 10 +/-1 ps at 31 K, allowing a more accurate measure of vibrational level spacings and decoherence time th an has been possible in frequency domain. The harmonic frequency of the mol ecule is reduced by 1.5 cm(-1) (0.7%) in the matrix. The lack of recurrence in the excited electronic state ensures that the resonant anti-Stokes scat tering arises only from the negative momentum component of the Raman packet . This momentum filter, which should be ubiquitous in condensed media, lead s to a signal with deeper modulation than in the gas phase. (C) 2001 Americ an Institute of Physics.