Yazar "Peng, W. X." 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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    Comment on "on the Ionisation and Dissociation of NO2 by Short Intense Laser Pulses"
    (ELSEVIER SCIENCE BV, 1998) Singhal, R. P.; Kılıç, Hamdi Şükür; Ledingham, K. W. D.; McCanny, Thomas; Peng, W. X.; Smith, Duncan J.; Kosmidis, C.
    Data for the dissociation and ionisation of NO, with laser intensities up to 2.3 X 10(14) W cm(-2) are presented. The effects of variation in intensity, wavelength and pulse width are discussed. For 90 fs pulse width the relative parent-ion yield is independent of the laser intensity at 750 nm but shows a weak dependence at 375 nm. The parent-ion yield is observed to increase as the laser pulse width decreases. The longer wavelength of 750 nm produces a larger parent-ion yield in comparison with 375 nm. This would suggest that pulse width and laser wavelength are important parameters in shea-pulse laser mass spectrometry.
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    Ionization and Dissociation of Benzaldehyde Using Short Intense Laser Pulses
    (AMER CHEMICAL SOC, 1998) Smith, D. J.; Ledingham, K. W. D.; Kılıç, H. S.; McCanny, T.; Peng, W. X.; Singhal, R. P.; Langley, A. J.; Kosmidis, C.
    In a recent series of experiments, femtosecond laser mass spectrometry (FLMS) was applied to benzaldehyde utilizing laser pulse widths in the range 90 fs to 2.7 ps. Beam intensities up to 2 x 10(14) W cm(-2) were used with wavelengths of 750 and 375 nm. Different ionization-dissociation channels were found compared with previous studies by other authors based in the nanosecond regime. The general theme emerging is one of predominant above-threshold ionization-dissociation (ID) in which predissociative states are largely bypassed via rapid optical up-pumping to the molecular ionization continuum. Above the parent ionization threshold, ladder-switching is seen to be a function of laser pulse width, intensity, and wavelength with exclusive parent ion formation being achievable in the lower intensity regions at all pulse widths. Increasing fragmentation occurs as the laser intensity increases, although parent supremacy remains. At 750 nm however, the increase of fragmentation with intensity is greatly reduced compared to 375 nm, leading to the conclusion that FLMS at longer wavelengths is preferred for chemical analysis. Moreover at 750 nm and at laser intensities close to 10(14) W cm(-2) C7H6O2+ becomes evident. It is also shown that the C7H6O+/C7H5O+ ratio is strongly dependent on the pulse width, suggesting that a hydrogen loss pathway has a dissociation time of about a picosecond.