Molecular dynamics of methylamine, methanol, and methyl fluoride cations in intense 7 micron laser fields.

Fragmentation and isomerization of methylamine (CH3NH2(+)), methanol (CH3OH(+)), and methyl fluoride (CH3F(+)) cations by short, intense laser pulses have been studied by ab initio classical trajectory calculations. Born-Oppenheimer molecular dynamics (BOMD) on the ground-state potential energy surface were calculated with the CAM-B3LYP/6-31G(d,p) level of theory for the cations in a four-cycle laser pulse with a wavelengths of 7 μm and intensities of 0.88 × 10(14) and 1.7 × 10(14) W/cm(2). The most abundant reaction path was CH2X(+) + H (63-100%), with the second most favorable path being HCX(+) + H2 (0-33%), followed by isomerization to CH2XH(+) (0-8%). C-X cleavage after isomerization was observed only in methyl fluoride. Compared to random orientation, CH3X(+) with the C-X aligned with the laser polarization gained energy nearly twice as much from laser fields. The percentage of CH3(+) + X dissociation increased when the C-X bond was aligned with the laser field. Alignment also increased the branching ratio for H2 elimination in CH3NH2(+) and CH3OH(+) and for isomerization in CH3OH(+).