Deformation of an inner valence molecular orbital in ethanol by an intense laser field

Valence molecular orbitals play a crucial role in chemical reactions. Here, we reveal that an intense laser field deforms an inner valence orbital (10a') in the ethanol molecule. We measure the recoil-frame photoelectron angular distribution (RFPAD), which corresponds to the orientation dependence of the ionization probability of the orbital, using photoelectron-photoion coincidence momentum imaging with a circularly polarized laser pulse. Ab initio simulations show that the orbital deformation depends strongly on the laser field direction and that the measured RFPAD cannot be reproduced without taking the orbital deformation into account. Our findings suggest that the laser-induced orbital deformation occurs before electron emission on a suboptical cycle time scale.

Selective bond breaking of CO2 in phase-locked two-color intense laser fields: laser field intensity dependence

One of the two equivalent C–O bonds of CO₂ can be selectively broken by phase-locked two-color intense laser fields.

Dissociation of H2NCH dication in a strong laser field

Ab initio classical molecular dynamics calculations have been used to simulate the dissociation of H(2)NCH(2+) in a strong laser field. The frequencies of the continuous oscillating electric field were chosen to be ω = 0.02, 0.06, and 0.18 au (2280, 760, and 253 nm, respectively). The field had a maximum strength of 0.03 au (3.2 × 10(13) W cm(-2)) and was aligned with the CN bond. Trajectories were started with 100 kcal/mol of vibrational energy above zero point and were integrated for up to 600 fs at the B3LYP/6-311G(d,p) level of theory. A total of 200 trajectories were calculated for each of the three different frequencies and without a field. Two dissociation channels are observed: HNCH(+) + H(+) and H(2)NC(+) + H(+). About one-half to two-thirds of the H(+) dissociations occurred directly, while the remaining indirect dissociations occurred at a slower rate with extensive migration of H(+) between C and N. The laser field increased the initial dissociation rate by a factor of ca. 1.4 and decreased the half-life by a factor of ca. 0.75. The effects were similar at each of the three frequencies. The HNCH(+) to H(2)NC(+) branching ratio decreased from 10.6:1 in the absence of the field to an average of 8.4:1 in the laser field. The changes in the rates and branching ratios can be attributed to the laser field lowering the reaction barriers as a result of a difference in polarizability of the reactant and transition states.

Theoretical investigation of the stability of highly charged C60 molecules produced with intense near-infrared laser pulses

We theoretically investigated the stability of highly charged C(60) (z+) cations produced from C(60) with an ultrashort intense laser pulse of lambda approximately 1800 nm. We first calculated the equilibrium structures and vibrational frequencies of C(60) (z+) as well as C(60). We then calculated key energies relevant to dissociation of C(60) (z+), such as the excess vibrational energy acquired upon sudden tunnel ionization from C(60). By comparing the magnitudes of the calculated energies, we found that C(60) (z+) cations up to z approximately 12 can be produced as a stable or quasistable (microsecond-order lifetime) intact parent cation, in agreement with the recent experimental report by V. R. Bhardwaj et al. [Phys. Rev. Lett. 93, 043001 (2004)] that almost only intact parent C(60) (z+) cations up to z=12 are detected by a mass spectrometer. The results of Rice-Ramsperger-Kassel-Marcus calculation suggest that the lifetime of C(60) (z+) drastically decreases by ten orders of magnitude as z increases from z=11 to z=13. Using the time-dependent adiabatic state approach, we also investigated the vibrational excitation of C(60) and C(60) (z+) by an intense near-infrared pulse. The results indicate that large-amplitude vibration with energy of >10 eV is induced in the delocalized h(g)(1)-like mode of C(60) (z+).