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Polarization dependent femtosecond pump-probe spectra display characteristic vibrational wave packet dynamics of ClF in Ar (isotropic cage and small fragment size) and I2 in Kr (cylindrical cage and large fragments). The intensity ratio of the signals for pumping with parallel versus crossed polarization with respect to the probe pulse is close to the value 1/3, as expected for full photoselection immediately after excitation. For ClF this ratio depolarizes to unity within τr=1.2 ps, showing the ultrafast randomization of the orientation of the molecular bond due to fragment scattering off the matrix cage. The direction of the I2 bond is geometrically fixed by the Kr matrix and the ratio remains constant.

The formation of the two ionic products of Cl+F− versus Arn+F− is controlled by variation of the time delay between two ultrafast UV pulses. The Arn+F− exciplex is characterized by a fluorescence band at 355 nm and the Cl+F− product by the D′ emission at 420 nm. In this Tannor–Kosloff–Rice control scheme, the pump pulse dissociates ClF in a solid argon matrix. During the early dynamics in the matrix cage the F fragments have sufficient kinetic energy to closely approach the Ar atoms. Here a control pulse, which is delayed by typically 3 ps, induces the ionic bond Arn+F−. Energy loss by collisions with the cage leads to recombination and vibrational relaxation in the B state of ClF. A control pulse delayed by 30–100 ps leads to exclusive formation of the ionic bond Cl+F−. A switching contrast better than 1 to 10 can be achieved in both directions. The control scheme makes use of the time scale of vibrational relaxation. By femtosecond pump–probe spectroscopy we show the wave packet oscillations from the re...

Vibrational progressions in the A′→X(v″) fluorescence of ClF in Ar and Kr matrices with 1

Photodissociation and recombination of an F2 molecule embedded in an Ar cluster is investigated. The electronic states involved are described by the valence bond approach for the F(2P)+F(2P) interaction, with spin–orbit coupling included and the anisotropic interactions between F and Ar atoms described by the diatomics-in-molecules (DIM) approach. The potential energy surfaces for 36 electronic states and the nonadiabatic couplings between them are constructed in this basis. The surface hopping method is used for dynamical simulations. The main results are: (i) Spin nonconserving transitions play a crucial role both in the dissociation and in the recombination dynamics. (ii) The ratio between the population of the triplet states and the population of the singlet states reaches the statistical equilibrium value of 3:1 60 fs after the photoexcitation, but the population of specific singlet and triplet states remains nonstatistical for at least 1.5 ps. (iii) Recombination on the only bound excited state (3Πu...

The many-body dynamics in the condensed phase often leads to structureless absorption spectra while vibrational recurrences in localized coordinates are preserved. A scheme is presented to directly extract anharmonicities and energy relaxation from the varying vibrational periods in pump–probe spectra. For the B state of I2 a constant anharmonicity and a vibrational energy relaxation rate decreasing by one order of magnitude in the wavelength range from 540 to 583 nm are obtained. An analytical expression for compensating the wave packet dispersion due to the anharmonicity is derived and it is applied to the control of wave packets by chirped pulses. Focusing of the wave packet is experimentally observed in accordance with the anharmonicity and even after significant energy relaxation. Predissociation rates are determined from the envelopes of the pump–probe spectra.