Alignment Of NO Research Articles

Adsorption site, orientation and alignment of NO adsorbed on Au(100) using 3D-velocity map imaging, X-ray photoelectron spectroscopy and density functional theory.

Nitric oxide adsorption on a Au(100) single crystal has been investigated to identify the type of adsorption, the adsorption site, and the orientation and alignment of the adsorbed NO relative to the surface. This was done using a combination of 3D-surface velocity map imaging, near-ambient pressure X-ray photoelectron spectroscopy, and density functional theory. NO was observed to be molecularly adsorbed on gold at ∼200 K. Very narrow angular distributions and cold rotational distributions of photodesorbed NO indicate that NO adsorbs on high-symmetry sites on the Au crystal, with the N-O bond axis close to the surface normal. Our density functional theory calculations show that NO preferentially adsorbs on the symmetric bridge (2f) site, which ensures efficient overlap of the NO π* orbital with the orbitals on the two neighbouring Au atoms, and with the N-O bond axis aligned along the surface normal, in agreement with our conclusions from the rotational state distributions. The combination of XPS, which reveals the orientation of NO on gold, with 3D-surface velocity map imaging and density functional theory thus allowed us to determine the adsorption site, orientation and alignment of nitric oxide adsorbed on Au(100).

Collision Energy Dependent Cross Section and Rotational Alignment of NO (A 2Σ+) in the Energy-Transfer Reaction of N2 (A3Σu+) + NO (X 2Π) → N2 (X 1Σg+) + NO (A 2Σ+)

We have studied the collision energy dependent cross section and alignment of NO (A (2)Σ(+)) rotation in the energy-transfer reaction of N2 (A (3)Σ(u)(+)) + NO (X (2)Π) → N2 (X (1)Σ(g)(+)) + NO (A (2)Σ(+)) at the collision energy (E) region of 0.03-0.2 eV. NO (A (2)Σ(+)) emission in two linear polarization directions in the collision frame (parallel (∥) and perpendicular (⊥) with respect to the relative velocity vector (vR)) has been measured as a function of collision energy. NO (A (2)Σ(+)) rotation (J-vector) turns out to be aligned perpendicular to vR. In addition, collision energy is found to enhance the degree of alignment of NO (A (2)Σ(+)) rotation. The collision energy dependent cross sections σ(∥,(⊥))(E) (excitation functions) show a rapid fall-off following an initial rise with a threshold less than 0.02 eV. The excitation function at the parallel alignment of NO (A (2)Σ(+)) rotation, σ(J∥v(R), (E), is slightly shifted to the low collision energy region as compared with σ(J ⊥ vR, E). We propose that the rapid fall-off feature in the excitation function is attributed to the multidimensional nonadiabatic transitions.

Rotational Alignment of NO (A2Σ+) from Collisions with Ne

We report the direct angle-resolved measurement of collision-induced alignment of short-lived electronically excited molecules using crossed atomic and molecular beams. Utilizing velocity-mapped ion imaging, we measure the alignment of NO in its first electronically excited state (A(2)Σ(+)) following single collisions with Ne atoms. We prepare A(2)Σ(+) (v = 0, N = 0, j = 0.5) and by comparing images obtained using orthogonal linear probe laser polarizations, we experimentally determine the degree of alignment induced by collisional rotational excitation for the final rotational states N' = 4, 5, 7, and 9. The experimental results are compared to theoretical predictions using both a simple classical hard-shell model and quantum scattering calculations on an ab initio potential energy surface (PES). The experimental results show overall trends in the scattering-angle dependent polarization sensitivity that are accounted for by the simple classical model, but structure in the scattering-angle dependence that is not. The quantum scattering calculations qualitatively reproduce this structure, and we demonstrate that the experimental measurements have the sensitivity to critique the best available potential surfaces. This sensitivity to the PES is in contrast to that predicted for ground-state NO(X) alignment.

Ion imaging studies of product rotational alignment in collisions of NO with Ar

Abstract The collision-induced rotational alignment of NO ( X 2 Π 1/2 , v=0, j=4.5 , 8.5, 11.5, 12.5, and 15.5) is measured for rotationally inelastic scattering of NO ( X 2 Π 1/2 , v=0, j=0.5) with Ar at 520 ± 70 cm−1 of center-of-mass collision energy. The experiments are performed by velocity-mapped ion imaging with polarized 1+1′ REMPI of the scattered NO product. Differential cross-sections (DCSs), corrected for alignment effects, are also reported. While the alignment correction is important, it does not change the positions of the observed rotational rainbows. The alignment moments and DCSs are compared with calculations using Alexander's CCSD(T) PESs. The theoretical and experimental DCSs show excellent agreement, as do the theoretical and experimental alignment moments for low Δj. For high Δj collisions and back-scattered trajectories, which sample the hard wall of the PES, the theoretical and experimental alignment moments show less agreement.

Collision-induced alignment of NO+ drifting in argon: Calculated distribution functions and microscopic quadrupole alignment parameters

Molecular dynamics simulations of NO+ drifting in argon are presented. In this system, the ion–bath gas mass ratio is close to but less than unity, thus increasing the importance of inelastic collisions. Strong velocity–angular momentum coupling is found, and in particular the quadrupolar alignment parameter as a function of the velocity parallel with the field takes on, with decreasing velocities, values that start as negative, become positive, and subsequently decay toward negative. To the best of our knowledge, this is the first report of the decay of this alignment towards negative values at the low end of the velocity distribution. The accuracy of an approximate distribution function [R. Baranowski and M. Thachuk, Phys. Rev. A 63, 032503 (2001)] is also examined in detail. It is found to give results that are generally qualitatively correct, and for many properties, semiquantitatively correct as well. The agreement, however, is not as good as that found for systems with ion–bath gas ratios greatly exceeding unity.

Ion imaging measurement of collision-induced rotational alignment in Ar-NO scattering

Collision-induced rotational alignment of NO X 2Π1/2(v=0,j=8.5) is measured for rotationally inelastic scattering of NO X 2Π1/2(v=0,j=0.5) with Ar at 65 meV collision energy. The experiments are performed by velocity-mapped ion imaging with polarized 1+1′ REMPI probing of the scattered NO products. It is shown that the azimuthal information intrinsic to imaging detection allows the measurement of additional alignment moments not previously reported. The measured alignment shows only qualitative agreement with the predictions of the kinematic apse conservation model.

Molecular-dynamics study of rotational alignment of NO+ drifting in helium—velocity and angular momentum distribution functions

Collision-induced rotational alignment of NO+ ions drifting in a helium buffer gas is studied with molecular dynamics using the ab initio potential surface of S. K. Pogrebnya et al. [Int. J. Mass Spectrom. Ion Proc. 149/150, 207 (1995)], obtained via a coupled-cluster singles–doubles approximation. We examine average translational and rotational temperatures, velocity and angular momentum distributions, and the dependence of these quantities on the applied electric field. The distributions show that angular momentum is preferentially aligned perpendicular to the electric field vector. We investigate the mechanism of this alignment through a multipolar moment expansion, and propose and demonstrate the accuracy of a bi-Maxwellian analytic form for describing the angular momentum distribution.

Probing the alignment of NO(X 2Π) by [2+1] resonance-enhanced multiphoton ionization via the C 2Π state: A test of semiclassical theory in 355 nm photodissociation of NO2

A theoretical method to analyze the two- and three-dimensional imaging data of photofragments with polarized angular momentum was tested by comparing with the experimental data on NO from 355 nm photodissociation of NO2. The alignment of NO(X 2Π) was detected by [2+1] resonance-enhanced multiphoton ionization via the C 2Π state. The data were analyzed by assuming the μ–ν–J triple vector correlation described by semiclassical multipole moments in the velocity-fixed frame. The geometrical factors for the two-photon absorption were derived rigorously for the intermediate coupling between Hund’s cases (a) and (b). It was also shown, however, that the geometrical factors for high J are independent of the coupling case and can be approximated by simple formulas. Excellent agreement between the simulation and the experimental data proved the validity of the semiclassical treatment.

Picosecond laser probing of rotational alignment of NO in CO2.

Picosecond laser probing of rotational alignment of NO in CO2.

Rotational alignment of NO from Pt(111). Inelastic scattering and molecular desorption

The rotational alignment distribution of NO has been measured subsequent to the molecule's interaction with a well characterized Pt(111) surface. Internal state distributions have been probed using 1 + 1 resonance-enhanced multiphoton ionization (REMPI) spectroscopy in which lines of the NO A 2Σ+–X2Π(0, 0) band constitute the resonant transition. NO/Pt(111) scattering has been studied in two distinct regimes: inelastic scattering and trapping/desorption. In both cases, there is relatively no preferential alignment of rotation for J < 12.5. However, molecules with higher rotational angular momentum show a marked increase in alignment. Inelastically scattered molecules prefer to rotate in a plane normal to the surface (‘cartwheel’ motion), whereas desorbing molecules prefer to rotate in a plane parallel to the surface (‘helicopter’ motion). These measurements provide new insight into momentum transfer at surfaces and the nature of the transition state which leads to molecular desorption.