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

Multiphoton ionisation/fragmentation of acetone has been studied at lambda = 355 nm using time-of-flight mass spectrometry. A broad peak at m/e = 43 i s observed which shows a three-photon laser power dependence. The results s uggest that three-photon ionisation at 355 nm produces vibrationally excite d 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 r egion. Under high laser intensity conditions, a bimodal distribution of m/e = 43 peak was observed which has been assigned to two different isomeric p roduct channels. The results provide clear evidence for partial isomerisati on of the keto form of the acetone radical cation to the enol form. On ioni sation at 355 nm, CH3COC2H5 fragments into two channels corresponding to (C H3CO+) and (C2H5CO+) in the ratio of approximately 3:1. (C) 1999 Elsevier S cience B.V. All rights reserved.