Comparative stereodynamics in molecule-atom and molecule-molecule rotational energy transfer: NO(A2Σ+) + He and D2

Abstract

We present a crossed molecular beam scattering study, using velocity-map ion-imaging detection, of state-to-state rotational energy transfer for NO(A(2)Σ(+)) in collisions with the kinematically identical colliders He and D2. We report differential cross sections and angle-resolved rotational angular momentum polarization moments for transfer of NO(A, v = 0, N = 0, j = 0.5) to NO(A, v = 0, N' = 3, 5-12) in collisions with He and D2 at respective average collision energies of 670 cm(-1) and 663 cm(-1). Quantum scattering calculations on a literature ab initio potential energy surface for NO(A)-He [J. Kłos et al., J. Chem. Phys. 129, 244303 (2008)] yield near-quantitative agreement with the experimental differential scattering cross sections and good agreement with the rotational polarization moments. This confirms that the Kłos et al. potential is accurate within the experimental collisional energy range. Comparison of the experimental results for NO(A) + D2 and He collisions provides information on the hitherto unknown NO(A)-D2 potential energy surface. The similarities in the measured scattering dynamics of NO(A) imply that the general form of the NO(A)-D2 potential must be similar to that calculated for NO(A)-He. A consistent trend for the rotational rainbow maximum in the differential cross sections for NO(A) + D2 to peak at more forward angles than those for NO(A) + He is consistent with the NO(A)-D2 potential being more anisotropic with respect to NO(A) orientation. No evidence is found in the experimental measurements for coincident rotational excitation of the D2, consistent with the potential having low anisotropy with respect to D2. The NO(A) + He polarization moments deviate systematically from the predictions of a hard-shell, kinematic-apse scattering model, with larger deviations as N' increases, which we attribute to the shallow gradient of the anisotropic repulsive NO(A)-He potential energy surface.

State-to-State Differential Cross Sections for Inelastic Collisions of NO Radicals with para-H2 and ortho-D2

“… 15 Luxford et al reported the state-to-state DCSs and angular resolved rotational angular momentum polarization moments for collisions of electronically excited NO( A 2 Σ) with D 2 . 16 Recently, de Jongh et al studied the DCS of NO + He and NO + ortho -D 2 with very high resolution as a function of the collision energy using a Stark decelerator, resolving diffraction oscillations in the angular distributions. Due to the larger size of D 2 , the differences in angular spacing between individual diffraction peaks were observed.…”

Stereodynamics of rotational energy transfer in NO(A2Σ+) + Kr collisions

“…We observed quantitative agreement between experiment and theory for NO(A) + He, and very good agreement for NO(A) + Ar. 25,27 There are larger discrepancies between QS calculations and experiment for NO(A) + Ne. 23,26 In particular, we observe a strong forward scattered peak in the 0-101 range in the experimental DCSs for a wide range of final rotational states, which is not reproduced by QS calculations.…”

“…However, following our initial demonstration of the combination of optical state preparation of NO(A) with crossed molecular beams and VMI detection, [20][21][22] we have performed a series of systematic experimental and theoretical studies of rotationally inelastic collisions of NO(A). [23][24][25][26][27] In these experiments we have measured both DCSs and angle-resolved rotational alignment moments for the NO(A) + He, Ne and Ar systems. We observed quantitative agreement between experiment and theory for NO(A) + He, and very good agreement for NO(A) + Ar.…”

“…In contrast to the relatively simple KA behaviour observed for the NO(X) + Rg scattering, all of the NO(A) + Rg systems studied to date show strong deviations from the KA model, in both experiment and theoretical results. 22,23,[25][26][27] A striking observation for collisions with Ne and Ar are strong, angle-dependent, deviations from the KA model, which are most pronounced at scattering angles close to the rainbow maxima in the DCS. Only in the backward scattering hemisphere, at angles greater than 1501, does the observed rotational alignment fit the KA model.…”

Imaging diffraction oscillations for inelastic collisions of NO radicals with He and D2

“…4 Recently, the DCSs, as well as the rotational polarization moments, have been measured for electronically excited NO(A 2 Σ + ) colliding with He and D 2 . 5 The NO-He system has been the subject of several highlevel ab initio studies and its PES is well-known. [6][7][8] The scattering cross sections computed with these PESs are generally in very good agreement with experimentally determined cross sections.…”