document: It has been known [9,14,18,22] that the fragmentation processes in polyatomic molecules induced by an intense ultrafast laser field can sometimes exhibit sensitive dependence on the instantaneous phase characteristics of the laser field. Depending on the change in sign the chirped laser pulses, fragmentation could be either enhanced or suppressed [14,18,22]. Controlling the outcome of such laser induced molecular fragmentation with chirped femtosecond laser pulses has brought forth a number of experimental and theoretical effects in the recent years. However, efforts are continuing for a specific fragment channel enhancement, which is difficult since it also is a function of the molecular system under study [20,22–24]. Here we report the observation of a coherently enhanced fragmentation pathway of n-propyl benzene, which seems to have such specific fragmentation channel available. We found that for n-propyl benzene, the relative yield of C3H3+ is extremely sensitive to the phase of the laser pulse as compared to any of the other possible channels. In fact, there is almost an order of magnitude enhancement in the yield of C3H3+ when negatively chirped pulses are used, while there is no effect with the positive chirp. Moreover, the relative yield of all the other heavier fragment ions resulting from interaction of the strong field with the molecule is not sensitive to the sign of the chirp, within the noise level.
extractive_keyphrases: channels chirp chirped femtosecond laser pulses chirped laser pulses fragmentation fragment channel enhancement heavier fragment ions intense ultrafast laser field laser field laser pulse molecular system molecule negatively chirped pulses polyatomic molecules
abstractive_keyphrases: c3h3+ fragmentation channel fragmentation processes laser induced molecular fragmentation n-propyl benzene observation of a coherently enhanced fragmentation pathway positive chirp