Formation and dissociation of protonated pyridine–methanol cluster ions at 355 and 266 nm

The multi-photon ionization process of the hydrogen-bond cluster of pyridine–methanol has been investigated using a conventional and reflectron time-of-flight mass spectrometer (RTOF-MS) at 355 and 266 nm laser wavelengths, respectively. The sequences of the protonated cluster ions (CH3OH)nH+ and (C5H5Nn)(CH3OH)mH+ (n=1,2) were observed at both laser wavelengths, while the sequence of the cluster ions (CH3)OHn(H2O)H+ was observed only at 355 nm laser wavelength. The difference between the relative signal intensities of the protonated methanol cluster ions at different laser wavelengths is attributed to different photoionization mechanisms. Some nascent cluster ions in metastable states dissociated during free flight to the detector. The dissociation kinetics is also discussed.