Measurements and Quasi-Quantum Modeling of the Steric Asymmetry and Parity Propensities in State-to-State Rotationally Inelastic Scattering of NO (²Π_1/2) with D₂

Abstract

Relative integrated cross sections are measured for spin-orbit-conserving, rotationally inelastic scattering of NO (2Pi1/2), hexapole-selected in the upper Lambda-doublet level of the ground rotational state (j = 0.5), in collisions with D2 at a nominal energy of 551 cm-1. The final state of the NO molecule is detected by laser-induced fluorescence (LIF). The state-selected NO molecule is oriented with either the N end or the O end toward the incoming D2 molecule by application of a static electric field E in the scattering region. This field is directed parallel or antiparallel to the relative velocity vector v. Comparison of signals taken for the different applied field directions gives the experimental steric asymmetry SA, defined by SA = (sigma v upward arrow downward arrow E - sigma v upward arrow upward arrow E)/(sigma v upward arrow downward arrow E + sigma v upward arrow upward arrow E), which is equal to within a factor of -1 to the molecular steric effect, Si-->f identical with (sigmaD2-->NO - sigmaD2-->ON)/(sigmaD2-->NO + sigmaD2-->ON). The dependence of the integral inelastic cross section on the incoming Lambda-doublet component is also measured as a function of the final rotational (jfinal) and Lambda-doublet (epsilonfinal) state. The measured steric asymmetries are similar to those previously observed for NO-He scattering. Spin-orbit manifold-conserving collisions exhibit a larger propensity for parity conservation than their NO-He counterparts. The results are interpreted in the context of the recently developed quasi-quantum treatment (QQT) of rotationally inelastic scattering [Gijsbertsen, A.; Linnartz, H.; Taatjes, C. A.; Stolte, S. J. Am. Chem. Soc. 2006, 128, 8777]. The QQT predictions can be inverted to obtain a fitted hard-shell potential that reproduces the experimental steric asymmetry; this fitted potential gives an empirical estimate of the anisotropy of the repulsive interaction between NO and D2. QQT computation of the differential cross section using this simple model potential shows reasonable agreement with the measured differential cross sections.

Tensor cross sections and the collisional evolution of state multipoles: OH(XΠ2)–Ar

“…Van Beck et al 9 observed orientational effects in OH͑X 2 ⌸͒ -Ar rotationally inelastic collisions in a crossed beam experiment, and differential and integral cross sections for reorientation of the molecular axis were determined as a function of the initial orientation. Stolte and co-workers 10,11 investigated the steric asymmetry in rotationally inelastic collisions of NO͑X 2 ⌸͒ with several collision partners.…”

The quasi-quantum treatment of rotationally inelastic scattering from a hard shell potential: its derivation and practical use

“…They were able to explain the remarkable fact that N-end (O-end) collisions are favoured for odd (even) changes in the rotational quantum number 16,19,26,27 . In addition, the existence of so-called parity pairs in the differential cross-sections was predicted by the QQT calculations and confirmed both experimentally and by exact quantum mechanical calculations.…”

“…It has a phase part e iη i→f (γa;β) that will give the interference between the contributions from the different directions of the molecular axis. And it has a magnitude g geom (γ a ; β) = |g i→f (γ a ; β)| that, when squared, should be equal to the "classical" or "geometrical" differential cross-section for a fixed molecule, see also appendix C or equation (19):…”

“…In addition, the existence of so-called parity pairs in the differential cross-sections was predicted by the QQT calculations and confirmed both experimentally and by exact quantum mechanical calculations. Very recently, Taatjes et al 19 used the QQT to obtain a hard shell potential energy surface for NO-D 2 by a fitting procedure using experimental data for the steric asymmetry of the integral cross-section. The QQT calculations of the differential cross-sections using this fitted potential show reasonable agreement with the measured differential cross-sections.…”

A new perspective: imaging the stereochemistry of molecular collisions

“…By comparison, the reactivity of side on attack was found to be much smaller. 105 20 75 The effect of molecular alignment of metastable CO(a 3 Π 1 ) (created using optical electronic excitation of CO(X 1 Σ + , v = 0, J = 0) using linearly polarized light) with NO has also been investigated.…”