The collisional depolarization of OH(A 2Σ+) and NO(A 2Σ+) with Kr

Abstract

Quantum beat spectroscopy has been used to measure rate coefficients at 300 K for collisional depolarization for NO(A (2)Σ(+)) and OH(A (2)Σ(+)) with krypton. Elastic depolarization rate coefficients have also been determined for OH(A) + Kr, and shown to make a much more significant contribution to the total depolarization rate than for NO(A) + Kr. While the experimental data for NO(A) + Kr are in excellent agreement with single surface quasiclassical trajectory (QCT) calculations carried out on the upper 2A(') potential energy surface, the equivalent QCT and quantum mechanical calculations cannot account for the experimental results for OH(A) + Kr collisions, particularly at low N. This disagreement is due to the presence of competing electronic quenching at low N, which requires a multi-surface, non-adiabatic treatment. Somewhat improved agreement with experiment is obtained by means of trajectory surface hopping calculations that include non-adiabatic coupling between the ground 1A(') and excited 2A(') states of OH(X/A) + Kr, although the theoretical depolarization cross sections still significantly overestimate those obtained experimentally.

Experimental and theoretical studies of the Xe–OH(A/X) quenching system

“…As in our previous work, [3][4][5]7,10,18,[33][34][35] the notation used here is as follows. In all cases, vectors are represented by bold italic symbols (j) and the corresponding quantum numbers by italics (j).…”

“…Non-adiabatic trajectory surface hopping 36 quasiclassical trajectory (TSH-QCT) calculations were run on the OH(X,A) + Xe potentials using the fewest switches surface hopping method of Tully. 37 Two kinds of calculations were performed: a two-state model, in which trajectories are propagated over the 1 2 A and 2 2 A potentials (ignoring 1 2 A ), as used in our recent work on OH + Kr; 8,18 and a full three-state model, including all the potential energy surfaces involved in this system (1 2 A , 1 2 A , and 2 2 A ) and the electronic and rotoelectronic couplings between them. 11 Full details of the two methods used are presented in Refs.…”

“…In contrast to previously studied systems such as OH(A) + He/Ar, [3][4][5][6][7]10 where the crossing between the excited a) Electronic mail: jklos@umd.edu b) Electronic mail: mark.brouard@chem.ox.ac.uk c) Electronic mail: aoiz@quim.ucm.es A 2 Σ + and ground X 2 Π potentials is located high on the repulsive wall, the OH(A) + Kr/Xe systems display conical intersections that are accessible at thermal collision energies. 8,11,18 For OH(A) + Kr, there is a region of significant coupling to the ground state close to the most attractive part of the excitedstate potential energy surface (PES), in the near-linear HO-Kr configuration, 8 and it is expected that the same or an even more pronounced feature will happen for the OH(A) + Xe system. In the case of collisions with Xe, the electronic quenching is even more efficient, with cross sections on the order of ≈20 Å 2 as compared with ≈8 Å 2 in the collisions with Kr.…”

Velocity map images from surface-hopping; reactive scattering of OH (2Σ+) + H2 (1Σ+g)

“…10 The popularity of this method makes it a natural choice for computational scientist to simulate, to effectively communicate results with experimentalist. We performed semi-classical trajectories on the potential energy surface (PES), used in similar systems to study quenching 11,12 and angular and velocity distributions. [13][14][15][16] Numerical quantum mechanical propagation and integration of these equations is a computationally intensive and hard to generalize.…”

Non-adiabatic quantum dynamics of the electronic quenching OH(A2Σ+) + Kr

“…[8][9][10][11][12] Among other processes involving electronic quenching with OH(A 2 S + ), collisions with rare gases (Rg) has received a special attention in the last few years as examples of processes in which collisional energy transfer and rotational depolarization may compete with electronic deactivation. [13][14][15][16][17][18][19][20][21][22][23] In addition, Rg + OH(A 2 S + ) collisions are amenable to rigorous electronic and dynamical calculations [16][17][18][19][21][22][23] that can be compared with a considerable amount of experimental information, ranging from thermal rate coefficients 7 and cross sections for selected spin-rotational initial states 5,6,18,19,21,23 to rotational and lambda-doublet state resolved cross sections. 21 Interestingly, whereas quenching cross sections for He, Ne, and Ar are almost negligible when compared with rotational energy transfer on the excited potential energy surface (PES), for Kr and Xe quenching cross sections are similar or larger than those with H 2 , O 2 , or N 2 .…”