Characterizing Multiphoton Excitation Using Time-Resolved X-ray Scattering

Molecular iodine is photoexcited by a strong 800-nm laser driving several channels of multiphoton excitation. The motion following photoexcitation is probed using time-resolved x-ray scattering, which produces a scattering map S(Q, tau). Temporal Fourier-transform methods are employed to obtain a frequency-resolved x-ray-scattering signal :(S) over tilde (Q, omega). Taken together, S(Q, tau) and :(S) over tilde (Q, omega) separate different modes of motion so that mode-specific nuclear oscillatory positions, oscillation amplitudes, directions of motion, and times may be measured accurately. Molecular dissociations likewise have a distinct signature, which may be used to identify both velocities and dissociation time shifts and also can reveal laser-induced couplings among the molecular potentials.