Bond-selective dissociation of polyatomic cations in mid-infrared strong fields.

Strong field-induced dissociation by intense mid-infrared pulses was investigated in bromofluoroform monocation (CF3Br(+)) and iodobenzene dication (C6H5I(2+)) using ab initio molecular dynamics calculations. In both systems, bond -selective dissociation was achieved using appropriate laser polarizations and wavelengths. For CF3Br(+), energetically disfavored fluorine elimination was strongly enhanced at wavelengths of 7 to 8 μm with polarization along a C-F bond. This is the result of two effects: the deposition of high enough kinetic energy into the molecule by the laser field and the near-resonant excitation of the C-F stretching mode. At shorter and off-resonant wavelengths, bromine elimination becomes significant due to rapid intramolecular vibrational energy redistribution (IVR). For C6H5I(2+), the branching ratios for the dissociation of the ortho-, meta-, and para-hydrogens can be controlled simply by changing the laser polarization. These results show the general applicability of bond selective dissociation of cations by intense mid-infrared laser fields.