The dissociative ionization and the Coulomb explosion of CH3I irradiated by a 35 fs 800 nm laser with a laser intensity of 4 x 10(13) to 6 x 10(14) W/cm2 was studied. In a relatively weak laser field (about 10(13) W/cm2), the dissociative ionization of CH3I took place. The speed distributions of the CH3+ and I+ fragments were measured and fitted using multiple Gaussian functions. Different product channels were found for CH3+ and I+, respectively. In a strong laser field (about 10(14) W/cm2), the multiply ionized fragment ions of Iq+ (q

Strong-field laser–molecule interaction forms much of the basis for initiating and probing ultrafast quantum dynamics. Previous studies aimed at elucidating the origins of vibrational coherences induced by intense laser fields have been confined to diatomic molecules. Furthermore, in all cases examined to date, vibrational wave packet motion is found to be induced by R-selective depletion; wave packet motion launched by bond softening, though theoretically predicted, remains hitherto unobserved. Here we employ the exquisite sensitivity of femtosecond extreme ultraviolet absorption spectroscopy to sub-picometer structural changes to observe both bond softening-induced vibrational wave packets, launched by the interaction of intense laser pulses with iodomethane, as well as multimode vibrational motion of the parent ion produced by strong-field ionization. In addition, we show that signatures of coherent vibrational motion in the time-dependent extreme ultraviolet absorption spectra directly furnish vibronic coupling strengths involving core-level transitions, from which geometrical parameters of transient core-excited states are extracted.

Light absorption by the photoreceptor microbial rhodopsin triggers trans-cis isomerization of the retinal chromophore surrounded by seven transmembrane α-helices. Sensory rhodopsin I (SRI) is a dual functional photosensory rhodopsin both for positive and negative phototaxis in microbes. By making use of the highly stable SRI protein from Salinibacter ruber (SrSRI), the early steps in the photocycle were studied by time-resolved spectroscopic techniques. All of the temporal behaviors of the Sn←S1 absorption, ground-state bleaching, K intermediate absorption, and stimulated emission were observed in the femto- to picosecond time region by absorption spectroscopy. The primary process exhibited four dynamics similar to other microbial rhodopsins. The first dynamics (τ1 ∼ 54 fs) corresponds to the population branching process from the Franck-Condon region to the reactive (S1(r)) and nonreactive (S1(nr)) S1 states. The second dynamics (τ2 = 0.64 ps) is the isomerization process of the S1(r) state to generate the ground-state 13-cis form, and the third dynamics (τ3 = 1.8 ps) corresponds to the internal conversion of the S1(nr) state. The fourth component (τ3' = 2.5 ps) is assignable to the J-decay (K-formation). This reaction scheme was further supported by the results of fluorescence spectroscopy. To investigate the protein response(s), the spectral changes of the tryptophan bands were monitored by ultraviolet resonance Raman spectroscopy. The intensity change following the K formation in the chromophore structure (τ ∼ 17 ps) was significantly small in SrSRI as compared with other microbial rhodopsins. We also analyzed the effect(s) of Cl(-) binding on the ultrafast dynamics of SrSRI. Compared with a chloride pump Halorhodopsin, Cl(-) binding to SrSRI was less effective for the excited-state dynamics, whereas the binding altered the structural changes of tryptophan following the K-formation, which was the characteristic feature for SrSRI. On the basis of these results, a primary photoreaction scheme of SrSRI together with the role of chloride binding is proposed.

The predissociation dynamics of B Rydberg state of methyl iodide has been studied with femtosecond two-color pump-probe time-of-flight spectra at pump pulse of 400nm and probe pulse 800 nm. The dominant product channels are the CH3I+ and CH3+ formation. The time-dependent signals for CH3I+ and CH3+ ions are obtained. Both of the signal curves can be fitted by biexponential decays with time constants of O 1 and O 2, O 1 was assigned to the lifetimes of high Rydberg states, which can be accessed by absorbing three 400 nm pump pulses and O 2 reflects the dynamics of B Rydberg state, which is accessed with two pump pulses. The lifetime of B Rydberg state is determined to be about 1.57 ps, which is incredibly consistent with the previous studies. The results were interpreted as a multiphoton dissociative ionization processes.