Experimental and theoretical studies have been carried out for nanosecond 355 nm laser induced dissociation/ionisation of dihalomethanes (CH2Cl2 and CH2Br2) using time of flight mass spectrometer. Both the molecules follow quite similar ionisation pattern and mass spectra showed H+, CH2+, X+, CX+, and CH2X+ as major ions with absence of parent ion peak. The energetics of different dissociation channels in the ground state of CH2X+/CH2X systems was investigated using ab initio calculations. Proposed mechanism involves dissociation of CH2X2 into CH2X, which then dissociates into several distinct competitive channels, products of which are subsequently ionised. (C) 2003 Elsevier B.V. All rights reserved.