Rotationally inelastic rates for N2–N2 system from a scaling theoretical analysis of the stimulated Raman Q branch

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.

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Computer simulations of the linewidth of the Raman Q-branch in fluid nitrogen

Michels

Scheerboom

Schouten

1995

“…[1][2][3] Similar experiments have been performed on mixtures of nitrogen with other gases, such as with helium 4 and, very recently, with argon. 5 Moreover, it turned out to be possible to simulate the vibrational behavior of nitrogen successfully with the help of molecular dynamical ͑MD͒ calculations.…”

Section: Introductionmentioning

confidence: 86%

The vibrational frequency of nitrogen near the fluid–solid transition in the pure substance and in mixtures

Michels

Kooi

Schouten

1998

. (1998). The vibrational frequency of nitrogen near the fluid-solid transition in the pure substance and in mixtures. Journal of Chemical Physics, 108(7), 2695-2702. DOI: 10.1063/1.475699 General rightsCopyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.• Users may download and print one copy of any publication from the public portal for the purpose of private study or research.• You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal ? Take down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. At high densities intramolecular vibrations are strongly dependent on the interactions with the surrounding molecules. In this paper a study is made of the consequences of these interactions on the Raman Q-branch of nitrogen. In particular the difference between a disordered and an ordered surrounding is surveyed. For this purpose, high-resolution Raman spectroscopy has been performed at room temperature on pure nitrogen as well as on a dilute mixture of nitrogen in argon, around the fluid-solid phase transition of these systems, which occur at Ϸ2.5 GPa and at Ϸ 1.3 GPa, respectively. Going from the liquid to the solid phase, a positive jump in the line shift and a dramatical drop in the linewidth are seen in both systems at the transition pressure. For a better understanding of the underlying mechanisms, molecular dynamical simulations have been performed on corresponding model systems. The results of these calculations are in fair agreement with the experimental data and reveal the reasons for the discontinuities. Although the average distance of the nearest neighbor molecules around the nitrogen molecule increases, the distance to the nearest neighbor molecules in line with the molecular axis of the nitrogen decrease at the phase transition. This results in a positive jump in the frequency. Further, the time-autocorrelation function of the vibration frequency has a long persisting positive tail in the fluid phase. This behavior is absent in the solid phase. Even more important is that this function has negative values during a substantial time interval in the solid phase. As a result, the correlation time is greatly reduced at the phase transition, which results in an important reduction of the linewidth as well. Finally, it is proven that also in the solid phase the nitrogen is really dissolved in argon.

“…͑10͔͒ along the jets. These values have been measured at fixed points corresponding to kinetic temperatures T t = 35, 28,22,18,14,10,8,6, and 4 K. At these points, which approximately span along the jet the domain of 1250ഛ z ഛ 14800 m, 40ജ T r ജ 7 K, and 15ϫ 10 22 ജ n ജ 4 ϫ 10 20 m −3 , the ratio,…”

Section: Discussionmentioning

confidence: 99%

Inelastic collisions in molecular nitrogen at low temperature (2⩽T⩽50K)

Fonfría¹,

Ramos²,

Thibault³

et al. 2007

Theory and experiment are combined in a novel approach aimed at establishing a set of two-body state-to-state rates for elementary processes ij → ᐉm in low temperature N 2 :N 2 collisions involving the rotational states i , j , ᐉ , m. First, a set of 148 collision cross sections is calculated as a function of the collision energy at the converged close-coupled level via the MOLSCAT code, using a recent potential energy surface for N 2 -N 2 . Then, the corresponding rates for the range of 2 ഛ T ഛ 50 K are derived from the cross sections. The link between theory and experiment, aimed at assessing the calculated rates, is a master equation which accounts for the time evolution of rotational populations in a reference volume of gas in terms of the collision rates. In the experiment, the evolution of rotational populations is measured by Raman spectroscopy in a tiny reference volume ͑Ϸ2 ϫ 10 −3 mm 3 ͒ of N 2 traveling along the axis of a supersonic jet. The calculated collisional rates are assessed experimentally in the range of 4 ഛ T ഛ 35 K by means of the master equation, and then are scaled by averaging over a large set of experimental data. The scaled rates account accurately for the evolution of the rotational populations measured in a wide range of conditions. Accuracy of 10% is estimated for the main scaled rates.