Collisional linebroadening in the atmosphere of light particles: problems and solutions in the framework of semiclassical treatmentстатья
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Дата последнего поиска статьи во внешних источниках: 26 сентября 2016 г.
Аннотация:Semiclassical approaches to the computation of spectral line parameters stay up to nowadays one of the working tools complementary
to refined but costly quantum-mechanical methods. Using of the trajectory concept together with quantum treatment of
internal molecular motions imposes however the hypothesis of rotation–translation decoupling and translational motion governed
by the isotropic potential. When a posteori justified for small heavy colliders, this hypothesis appears as doubtful for long polyatomic
molecules. At the same time, purely classical methods, even requiring the artificial procedure of the correspondence principle with
quantum mechanics, easily take into account the rototranslational energy transfer through the trajectory governed by the full anisotropic
potential. The infrared line broadening of a typically classical C2H2–Ar system at various temperatures is analyzed here from
these two different points of view. When a refined ab initio potential is chosen to represent the interaction energy, the semiclassical
approach leads to a visible overestimation of the line broadening for all values of the rotational quantum number and for all temperatures
studied whereas the fully classical treatment gives a quite satisfactory prediction. These fully classical computations show
that even for C2H2–Ar the rototranslational coupling is quite important, and variations of the translational motion parameters during
collisions produce detectable changes in rotation. When, for the sake of a meaningful comparison with the semiclassical
approach, the isotropic trajectories are imposed within the classical method, this leads to smaller line widths; the effect strongly
depends, however, on the peculiarities of potential energy surface, temperature, and rotational quantum number value