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  • Küçük Resim
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    Behavior of Polyatomic Molecules in Intense Infrared Laser Beams
    (American Chemical Society, 1998) Ledingham, K. W. D.; Singhal, R. P.; Smith, D. J.; McCanny, T.; Graham, P.; Kılıç, H. Ş.; Peng, W. X.; Wang, S. L.; Langley, A. J.; Taday, P. F.; Kosmidis, C.
    In the present Letter we report that a number of polyatomic molecules (M) when irradiated with short pulse lasers <90 fs at 750-790 nm and intensities up to 1015 W cir-2 produce multiply charged parent ions and do not fragment to any great degree. This surprising observation is found in both linear and ring structured molecules and is very similar to the behavior of inert atoms such as xenon under the same irradiation conditions. This is a very different behavior from irradiating with nanosecond pulses at 109 W cm-2 where low-mass fragments dominate the spectrum. For the hydrocarbon molecules presented in this work, there exists an envelope of 2+ ionized peaks, which corresponds to the parent and a number of (M -nH) satellites. This feature is characteristic of these molecules in the intensity region 1014-15 W cm-2 and is interpreted as evidence for tunneling or barrier suppression. Coulomb explosion leading to multiply charged atoms, which is evident for CS2, does not seem to be operating for the larger hydrocarbon molecules.
  • Küçük Resim
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    The Onset of Coulomb Explosions in Polyatomic Molecules
    (1999) Smith, D.J.; Ledingham, K. W. D.; Singhal, R. P.; McCanny, T.; Graham, P.; Kilic, H. S.; Tzallas, P.; Kosmidis, C.; Langley, A. J.; Taday, P. F.
    With the development of high intensity femtosecond lasers, the ionisation and dissociation dynamics of molecules has become an area of considerable interest. Using the technique of femtosecond laser mass spectrometry (FLMS), the molecules carbon disulphide, pyrimidine, toluene, cyclohexanone and benzaldehyde are studied with pulse widths of 50 fs in the near infrared (IR) wavelength region (790 nm). Results are presented and contrasted for laser beam intensities around 1015 and 1016W cm-2. For the lower intensities, the mass spectra yield dominant singly charged parent ions. Additionally, the appearance of doubly charged parent ions is evident for carbon disulphide, 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 increasing the laser intensity to ~1016 W cm-2, parent ion dominance decreases and the appearance of multiply charged atomic species occurs, particularly carbon. This phenomenon has been attributed to Coulomb explosions in which the fast absorption of many photons may produce transient highly ionised parent species which can subsequently blow apart.