General rightsIt is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), other than for strictly personal, individual use, unless the work is under an open content license (like Creative Commons). Disclaimer/Complaints regulationsIf you believe that digital publication of certain material infringes any of your rights or (privacy) interests, please let the Library know, stating your reasons. In case of a legitimate complaint, the Library will make the material inaccessible and/or remove it from the website. Please Ask the Library: http://uba.uva.nl/en/contact, or a letter to: Library of the University of Amsterdam, Secretariat, Singel 425, 1012 WP Amsterdam, The Netherlands. You will be contacted as soon as possible. By means of molecular dynamical simulations, the width of the Raman line in fluid N 2 is calculated at room temperature and pressures up to the melting line. The results are compared with experimental results for the linewidth and for the dephasing time. Detailed information is given about the relaxation mechanism of the vibrational frequency. For instance, a marked influence of the vibration-rotation coupling is seen, in particular at high pressures. Moreover, the time correlation function of the frequency reveals a long time behavior at high pressures. From a comparison of the simulated change in vibrational frequency as a function of pressure with experimental data for the line shift, an estimate is made for the contribution of the so-called ''attractive part'' to that shift.

Anomalous behavior of the vibrational-spectrum of the high-pressure delta-phase of nitrogen : a second-order transition Scheerboom, M.I.M.; Schouten, J.A.

To investigate the interaction between the water framework and a guest molecule in a clathrate hydrate, high-pressure Raman scattering experiments on nitrogen guest molecules have been performed. The pressure dependence of the N2 vibron(s) at room temperature (295 K) has been determined and a new phase transition has been discovered at 0.84 GPa.

In this paper the results of an experimental study of the vibrational Raman shift of solid δ-, ε-, and β-nitrogen will be presented. The measurements have been performed in a diamond anvil cell, from 0.5 to 14 GPa and from 120 to 400 K. The accuracy of the spectroscopic measurements has been optimized in order to determine the Raman shift as a function of temperature on an isobar. As will be shown, measurements along an isobar are appropriate for obtaining information about the orientational behavior of the molecules. In this study the results of β-nitrogen will be compared with those of δ- and ε-nitrogen. In β-nitrogen the Raman shift as a function of pressure shows a remarkable curvature, as compared to the results in δ- and ε-nitrogen. Also in contrast to the behavior in the other phases, in β-nitrogen the slope of the shift versus the temperature on an isobar changes from negative to positive when the pressure is increased. It will be argued that these results might be due to a short range orientational ordering of the molecules, as predicted by recent computer simulations. This ordering might cause a resonance coupling effect, resulting in a negative effect on the Raman shift in β-nitrogen.