Multiphoton ionisation of acetone at 355 nm: a time-of-flight mass spectrometry study

Multiphoton ionisation/fragmentation of acetone has been studied at λ=355 nm using time-of-flight mass spectrometry. A broad peak at m/e=43 is observed which shows a three-photon laser power dependence. The results suggest that three-photon ionisation at 355 nm produces vibrationally excited acetone ions which undergo fast dissociation. The broadening of the m/e=43 peak is found to depend on the laser power in the low laser intensity region. Under high laser intensity conditions, a bimodal distribution of m/e=43 peak was observed which has been assigned to two different isomeric product channels. The results provide clear evidence for partial isomerisation of the keto form of the acetone radical cation to the enol form. On ionisation at 355 nm, CH3COC2H5 fragments into two channels corresponding to (CH3CO+) and (C2H5CO+) in the ratio of approximately 3:1.