Dissociative ionization of ethanol by 400 nm femtosecond laser pulses

The dissociative ionization of ethanol in short-pulsed laser fields at ∼400 nm is investigated. The yield ratio of the C-O bond breaking with respect to the C-C bond breaking increases sharply as the temporal width increases from 60 to 400 fs, and the yield ratio is two to three times as large as that at 800 nm in the entire pulse-width range of 60-580 fs. The enhancement of the C-O bond breaking of singly charged ethanol at 400 nm and the bond elongation prior to the Coulomb explosion of doubly charged ethanol occurring in the relatively weak light field intensity of 1012 - 1013 W cm2 is interpreted by the efficient light-induced coupling among the electronic states at the shorter wavelength of 400 nm. From the double pulse experiment, in which ethanol is irradiated with a pair of short pulses (<80 fs), the most efficient coupling occurs at Δt=160 fs that is much earlier than Δt=250 at 800 nm, where Δt denotes the temporal separation of the two pulses, indicating that the nonadiabatic field-induced potential crossings of singly charged ethanol occurs much earlier at 400 nm than at 800 nm.