Narrow Results

The laser control of photodissociation branching in a diatomic molecule is demonstrated to be effectively achieved with use of the complete reflection phenomenon. The phenomenon and the control condition can be nicely formulated by the semiclassical (Zhu–Nakamura) theory. The method is applied to the branching between I(²P_3/2) (HI → H + I) and I*(²P_1/2) (HI → H + I*) formation, and nearly complete control is shown to be possible by appropriately choosing an initial vibrational state and laser frequency in spite of the fact that there are three electronically excited states involved. Numerical calculations of the corresponding wavepacket dynamics confirm the results.

The interference of dissociating wave packets for the Br₂ molecule in femtosecond laser field is studied theoretically using time-dependent quantum wave packet method. The interference of dissociating wave packets can be determined by the spectrum of laser field. By shaping laser pulses in frequency domain, the corresponding R- and v-dependent density functions can be effectively controlled. Compared with the 2-pulse excitation scheme, the resolution of the interference patterns can be improved by using 3- and 4-pulse excitation schemes. The dissociating velocity can be steered by varying laser parameters.

We have theoretically studied the photodissociation spectroscopy of Ca⁺-formaldehyde complex using the TD-B2-PLYP method. The SDD pseudopotential and basis sets for Ca and 6-31++G (2df, 2pd) basis sets for C, H, and O atoms were employed in all calculations. In this way, we have reassigned the photodissociation spectroscopy of this complex. All experimentally observed spectral features can be well explained by our calculation. Besides the charge–dipole interaction, a strong molecule–orbital interaction also exists in the excited states and plays an important role in photoexcitation of the Ca⁺–CH₂O complex.

A theoretical treatment is presented for the nonadiabatic photodissociation of hydroxyl radical. Five electronic states, X²Π, A²Σ⁺, 1⁴Σ^-, 1²Σ^- and 1⁴Π, are included in this simulation. Based on the accurate ab initio calculations of the potential energy curves, transition dipole moments and nonadiabatic couplings between the relevant states, the dissociation dynamics are investigated using the time-dependent quantum wave packet approach. The direct dissociation, following the excitation from the specific vibrational levels of the ground state X²Π to the repulsive state 1²Σ^- is examined, where the total and partial cross sections and the branching fractions of spin–orbit fine-structures of O(³P_J) are calculated over a wide range of the incident photon frequencies. For the predissociation via the bound excited state A²Σ⁺, the influence of the nonadiabatic interactions in different internuclear regions and the role of the repulsive states in the dissociation starting at different vibrational levels are also analyzed through the spin–orbit branching fractions of products.

The following sections are included:

• Introduction

• Experimental

• Photochemistry
  • Dimethyl Sulfoxide
  • Substituted Ethylenes
    • Acrylonitrile
    • Vinyl Chloride
  • Oxalyl Chloride
  • Propyne and Allene

• Reactive Scattering
  • Crossed-Beam Reaction Dynamics: Cl + Propane
  • CI + n-Pentane

• Conclusion

• Acknowledgments

• References