Stereodynamics in NO(X) + Ar inelastic collisions

Abstract

The effect of orientation of the NO(X) bond axis prior to rotationally inelastic collisions with Ar has been investigated experimentally and theoretically. A modification to conventional velocity-map imaging ion optics is described, which allows the orientation of hexapole state-selected NO(X) using a static electric field, followed by velocity map imaging of the resonantly ionized scattered products. Bond orientation resolved differential cross sections are measured experimentally for a series of spin-orbit conserving transitions and compared with quantum mechanical calculations. The agreement between experimental results and those from quantum mechanical calculations is generally good. Parity pairs, which have previously been observed in collisions of unpolarized NO with various rare gases, are not observed due to the coherent superposition of the two j = 1/2, Ω = 1/2 Λ-doublet levels in the orienting field. The normalized difference differential cross sections are found to depend predominantly on the final rotational state, and are not very sensitive to the final Λ-doublet level. The differential steric effect has also been investigated theoretically, by means of quantum mechanical and classical calculations. Classically, the differential steric effect can be understood by considering the steric requirement for different types of trajectories that contribute to different regions of the differential cross section. However, classical effects cannot account quantitatively for the differential steric asymmetry observed in NO(X) + Ar collisions, which reflects quantum interference from scattering at either end of the molecule. This quantum interference effect is dominated by the repulsive region of the potential.

Probing the location of the unpaired electron in spin–orbit changing collisions of NO with Ar

“…23 Molecular orientation, in which a specific end or side of a molecule can be directed towards a collision partner, is most widely achieved through hexapole state selection coupled with adiabatic passage into a static electric [40][41][42]45,46 or magnetic 43,44,47 field. The good agreement between experimental and calculated steric preferences obtained in studies of inelastic collisions of state selected NO(X) with Ar and He atoms [40][41][42][48][49][50][51] have confirmed the accuracy of the NO(X) + He/Ar ground electronic PESs, [52][53][54] while (unoriented) scattering experiments of electronically excited NO(A) with Ne 17 pointed to shortcomings in the calculated PESs. 55,56 Electric field orientation requires the molecule to be oriented to posses a permanent dipole moment and, if only the dominant first-order Stark effect is taken into account, to be open-shell.…”

“…We attribute the reduced quality of the fitted data for these particular states to the fact that the main features overlap with the region where the laboratory velocity is close to zero and the detection efficiency is highest. 49,72 As a consequence, any small inaccuracies in the instrument function will lead to noticeable deviations from the true DCS.…”

Direct observation of product-pair correlations in rotationally inelastic collisions of ND3 with D2

“…These experimental studies have been pivotal to test and develop theory, in order to calculate accurate potential energy surfaces (PESs) and to perform quantum scattering calculations using these PESs. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] Studies of collision energy transfer find applications in various research areas. In astrophysics, for example, the estimation of molecular abundances in the interstellar medium (ISM) from spectral line data requires collisional rate coefficients of various molecules with the most abundant interstellar species such as He, H and H 2 .…”

Correlated energy transfer in rotationally and spin–orbit inelastic collisions of NO(X2Π1/2, j = 1/2f) with O2(X3Σg−)

“…Furthermore, we study rotational excitation of NO within the X 2 P 1/2 (F 1 ) manifold, but we also study spin-orbit changing transitions to the X 2 P 3/2 (F 2 ) manifold that is located 123 cm À1 above the F 1 manifold. As is well-known from studies of RET in collisions between NO and rare gas atoms or simple molecules, [15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32] the interaction between NO and its collision partner is governed by two nonadiabatically coupled PESs. Spin-orbit conserving F 1 -F 1 transitions probe the average of the two PESs, whereas spinorbit changing F 1 -F 2 transitions are governed by the difference of the two PESs.…”