Coherent vibrations in methanol cation probed by periodic H3+ ejection after double ionization

When hydrocarbon molecules are exposed to an intense laser field, triatomic hydrogen molecular ion, H-3(+), is ejected. Here we describe pump-probe measurements of the ejection of H-3(+) from methanol dication with high temporal resolution using intense few-cycle laser pulses and find a long-lasting periodic increase in the yield of H-3(+). We show that H-3(+) ejection is the lowest energy decomposition channel and that its yield is enhanced each time when the vibrational wave packet coming back to the inner turning point of methanol cation is projected onto the dication potential energy surface. We also show that the time-resolved measurement of the yield of H-3(+) is an efficient tool not only for probing ultrafast nuclear dynamics of hydrocarbon cations but also for deriving vibrational frequencies of hydrocarbon cations with high precision.