The onset of coulomb explosions in polyatomic molecules

With the development of high intensity femtosecond lasers, the ionisation a nd dissociation dynamics. of molecules has become an area of considerable i nterest. Using the technique of femtosecond laser mass spectrometry (FLMS), the molecules carbon disulphide, pyrimidine, toluene, cyclohexanone and be nzaldehyde are studied with pulse widths of 50 fs in the near infrared (IR) wavelength region (790 mm), Results are presented and contrasted for laser beam intensifies around 10(15) and 10(16) W cm(-2). For the lower intensit ies, the mass spectra yield dominant singly charged parent ions. Additional ly, the appearance of doubly charged parent ions is evident for carbon disu lphide, toluene and benzaldehyde with envelopes of doubly charged satellite species existing in these local regions. Carbon disulphide also reveals a small triply charged component, Such atomic-like features are thought to be a strong fingerprint of FLMS at these intensities, However, upon increasin g the laser intensity to similar to 10(16) W cm(-2), parent ion dominance d ecreases and the appearance of multiply charged atomic species occurs, part icularly carbon. This phenomenon has been attributed to Coulomb explosions in which the fast absorption of many photons may produce transient highly i onised parent species which can subsequently blow apart. Copyright (C) 1999 John Wiley & Sons, Ltd.