Deuterium isotope effect on the radiatively induced unimolecular dissociation of small cluster ions

The slow, low pressure, unimolecular dissociation reactions of the weakly bound cluster ions, [(CH3)2CO]·Cl−,(C6H6·Cl− and (CH3OCH3)n·H3O+ (n = 2, 3), and their deuterated analogues have been examined by Fourier transform ion cyclotron resonance spectrometry. The unimolecular dissociation rate constant is found to be faster, in all cases, for the deuterium-substituted species; however the magnitude of this increase is ligand and cluster dependent. This observation is attributed to the vibrational frequency shifts of the infrared absorptions of each of the ligand species upon deuteration. The results obtained provide further support for the black-body radiation induced, unimolecular dissociation mechanism for weakly bound cluster ions at low pressure.