Integral steric asymmetry in the inelastic scattering of NO(X2Π)

Abstract

The integral steric asymmetry for the inelastic scattering of NO(X) by a variety of collision partners was recorded using a crossed molecular beam apparatus. The initial state of the NO(X, v = 0, j = 1/2, Ω=1/2, ϵ=-1,f) molecule was selected using a hexapole electric field, before the NO bond axis was oriented in a static electric field, allowing probing of the scattering of the collision partner at either the N- or O-end of the molecule. Scattered NO molecules were state selectively probed using (1 + 1') resonantly enhanced multiphoton ionisation, coupled with velocity-map ion imaging. Experimental integral steric asymmetries are presented for NO(X) + Ar, for both spin-orbit manifolds, and Kr, for the spin-orbit conserving manifold. The integral steric asymmetry for spin-orbit conserving and changing transitions of the NO(X) + O system is also presented. Close-coupled quantum mechanical scattering calculations employing well-tested ab initio potential energy surfaces were able to reproduce the steric asymmetry observed for the NO-rare gas systems. Quantum mechanical scattering and quasi-classical trajectory calculations were further used to help interpret the integral steric asymmetry for NO + O. Whilst the main features of the integral steric asymmetry of NO with the rare gases are also observed for the O collision partner, some subtle differences provide insight into the form of the underlying potentials for the more complex system.

Steric Effects in the Inelastic Scattering of NO(X) + Ar: Side-on Orientation

“…This indicates the transition from the quantum regime to the classical regime occurs around ∆j = 14. Similarly to the observed preference for scattering from the N-end of the NO molecule in the end-on orientation, represented in Figure 6b, 12,13,44,58,59 this +x preference for high ∆j values can be rationalised by a larger torque achievable at a larger distance from the center of mass (i.e. at the N-end) and necessary for high rotational excitations.…”

“…A much more detailed description of this technique is given elsewhere. 13,34,44 The product NO molecules are then state-selectively ionised using (1 + 1 ) REMPI; a probe laser (at approximately 226 nm) is tuned to the individual rotational line of the NO(A←X) transition, followed by ionisation using 308 nm light from a XeCl excimer laser.…”

“…The basis sets described above were then used to t the experimental images in Fourier space using a genetic algorithm, which is described elsewhere. 37,38,50 The ±x DCSs were retrieved by substituting the experimentally determined R The integral steric asymmetry, which has been previously dened for orientation with respect to the z-axis, 12,13,32,44,57 may be dened for orientation with respect to the x-axis according to…”

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

“…3 shows the experimental ISA (blue) along with the collision energy averaged QM ISA (red) for the x-axis orientation from the current experiment (top panel) and, for comparison, the z-axis orientation from previous work in our group. 85 As with the DCSs, there is good agreement between the experimental and QM calculated ISAs, and the alternation in preference between odd and even Dj is evident. However, in both the side-on and the end-on configurations, the N-side/ N-end preference is significantly larger in magnitude than the preference for the O-side/O-end.…”

“…The experimentally measured ISA is shown in blue, with error bars representing one standard deviation; the corresponding QM data, which have been averaged over the experimental collision energy distribution, are shown in red. The top panel is for the x-axis configuration, probed in the current experiment, and the bottom panel is for the z-axis orientation (with the experimental data taken from ref 85)…”