Yazar "Taday, P. F." seçeneğine göre listele

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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.
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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.
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    Time of Flight Mass Spectrometry of Aromatic Molecules Subjected to High Intensity Laser Beams
    (JOHN WILEY & SONS LTD, 1998) Smith, D. J.; Ledingham, K. W. D.; Singhal, R. P.; Kılıç, H. S.; McCanny, T.; Langley, A. J.; Taday, P. F.
    The recent introduction of femtosecond technology to pulsed lasers has led to the development of femtosecond laser mass spectrometry (FLMS), The present paper describes an FLMS investigation of the aromatic molecules, benzene, toluene and naphthalene. Wavelengths of 750 and 375 nm were used with beam intensities up to 4 x 10(14) W cm(-2). Pulse widths were of the order of 50-90 fs, The laser system was coupled to a linear time-of-flight mass spectrometer, This experimental method of chemical analysis is gaining momentum, often replacing its nanosecond forerunner, resonant enhanced multiphoton ionization, For the said molecules, predominant parent ion production is found, making identification unambiguous. In fact this characteristic is being consistently attained in small to medium mass molecules irradiated under similar conditions, leading to the conclusion that a universal chemical detection system is a possibility, Such soft ionization is particularly evident at longer wavelengths (similar to 750 nm) with less relative fragmentation, daughter ion formation, compared to results at shorter wavelengths (similar to 375 nm), In terms of parent ion formation, similar numbers are produced with laser intensities around 10(14) W cm(-2) for both wavelengths. It has also been shown that at a threshold of about 5 x 10(13) W cm(-2), double ionized molecules appear for the 750 nm wavelength. These interesting new mass spectra display intense single, double and even triple ionized peaks without significantly increased dissociation, Such effects are less pronounced at 375 nm..