Collisional angular momentum depolarization of OH(A) and NO(A) by Ar: A comparison of mechanisms

Abstract

This paper discusses the contrasting mechanisms of collisional angular momentum depolarization of OH(A(2)Σ(+)) and NO(A(2)Σ(+)) by Ar. New experimental results are presented for the collisional depolarization of OH(A) + Ar under both thermal and superthermal collision conditions, including cross sections for loss of both angular momentum orientation and alignment. Previous work on the two systems is summarized. It is shown that NO(A) + Ar depolarization is dominated by impulsive events in which the projection of the angular momentum, j, along the kinematic apse, a, is nearly conserved, and in which the majority of the trajectories can be described as "nearside." By contrast, at the relatively low collision energies sampled at 300 K, OH(A) + Ar depolarization is dominated by attractive collisions, which show a preponderance of "farside" trajectories. There is also evidence for very long-lived, complex type trajectories in which OH(A) and Ar orbit each other for several rotational periods prior to separation. Nevertheless, there is still a clear preference for conservation of the projection of j along the kinematic apse for both elastic and inelastic collisions. Experimental and theoretical results reveal that, as the collision energy is raised, the depolarization of OH(A) by Ar becomes more impulsive-like in nature.

Parity-Dependent Rotational Energy Transfer in CN(A2Π, ν = 4, j F1ε) + N2, O2, and CO2 Collisions

“…Similarly, comparison of experimental RET in OH(A) + Kr and QCT and QS calculations on an ab initio PES provided excellent agreement, despite the neglect of the electronic quenching channel in the calculations. 52 This suggests that more dynamically sensitive measurements are required to probe the geometry of reaction and quenching within the inelastically scattered products, such as the transfer of rotational angular momentum polarization 57,58 or measurements of differential scattering cross sections and product rotational angular momentum polarization. 59−61 …”

Semiclassical model for the distribution of final polar angles and m′ states in rotationally inelastic collisions

“…Information about transitions from states jm to j ′ m ′ is critical for a detailed understanding of the collisional transfer of orientation and alignment and of the alignment of molecules by laser pulses [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19]. Our recent calculations [20] addressed this issue; we reported fully quantum mechanical calculations for collisions of NaK (A 1 Σ + ) with He, including the Grawert coefficients [1] necessary to calculate transition cross sections σ(jm → j ′ m ′ ).…”

Theoretical calculations of rotationally inelastic collisions of He with NaK(A 1Σ+): Transfer of population, orientation, and alignment

“…Rate coefficients for the transfer of population in collisions of various diatomic molecules with rare gas perturbers have been of interest for many years, 2 but most measurements average the transitions jm → j ′ m ′ over m and m ′ . The measurements of Wolfe et al 1 and experimental and theoretical work in other labs [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] that investigates the evolution of orientation and alignment during collisions provide a great deal of additional, detailed information about changes in m as well as j. The work presented here draws on that foundation.…”