Controlling Chemical Reactions by Short, Intense Mid-Infrared Laser Pulses: Comparison of Linear and Circularly Polarized Light in Simulations of CICHO+ Fragmentation

Enhanced mode selective fragmentation of oriented ClCHO+ -> Cl + HCO+, H + ClCO+, HCl+ + CO with linear polarized intense mid-IR pulses was demonstrated in our previous computational study (J. Phys. Chem. Lett. 2012, 3, 2541). Simulations of angle-dependent strong field ionization of ClCHO indicate the ionization rate in the molecular plane is nearly twice as large as perpendicular to the plane, suggesting a degree of planar alignment can be obtained experimentally for ClCHO+, starting from neutral molecules. Classical trajectory calculations with a 4 cycle 7 mu m laser pulse (peak intensity of 1.26 x 10(14) W/cm(2)) show that circularly polarized light with the electric field in the plane of the molecule deposits more energy and yields larger branching ratios for higher energy fragmentation channels than linearly polarized light with the same maximum field strength. These results suggest circularly polarized mid-IR pulses can not only achieve control on reactions but also provide an experimentally accessible implementation.