Surface-hopping trajectories for OH(A2Σ+) + Kr: Extension to the 1A″ state

Abstract

We present a new trajectory surface hopping study of the rotational energy transfer and collisional quenching of electronically excited OH(A) radicals by Kr. The trajectory surface hopping calculations include both electronic coupling between the excited 2(2)A' and ground 1(2)A' electronic states, as well as Renner-Teller and Coriolis roto-electronic couplings between the 1(2)A' and 1(2)A″, and the 2(2)A' and 1(2)A″ electronic states, respectively. The new calculations are shown to lead to a noticeable improvement in the agreement between theory and experiment in this system, particularly with respect to the OH(X) rotational and Λ-doublet quantum state populations, compared with a simpler two-state treatment, which only included the electronic coupling between the 2(2)A' and 1(2)A' states. Discrepancies between the predictions of theory and experiment do however remain, and could arise either due to errors in the potential energy surfaces and couplings employed, or due to the limitations in the classical treatment of non-adiabatic effects.

Product lambda-doublet ratios as an imprint of chemical reaction mechanism

“…This angle connects the symmetry of the PES to that of the Λ-doublet state and, in the high j ′ limit, can be identified with θ j′u , the angle between the rotational angular momentum, j′ , perpendicular to the OD rotation plane and the vector u perpendicular to the three-atom plane19 (see Supplementary Fig. 1).…”

“…This is straightforward in the quasiclassical trajectories (QCT) framework19, where θ j′u can be computed at every step of the trajectory. In a pure quantum mechanical (QM) context, the equivalent magnitude would be , where is the projection of the rotational angular momentum along the u vector.…”

“…In fact, θ j ′ u represents the dihedral angle between the molecular plane, and the three-atom plane. As pointed out in refs 15, 19, can be used to relate the symmetry of the Λ-doublet levels to the symmetry of the PES.…”

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 .…”

“…18,21,23 As such, adiabatic calculations carried out on the 2A 0 excited PES for Kr and Xe cannot account for rotational initial state depopulation. [21][22][23] Previous calculations for the Kr + OH(A 2 S + ) system using quasiclassical trajectories (QCT) and surface hopping (SH) on ab initio PESs 21,22 demonstrated that the sole consideration of 2-PES transition (2A 0 -1A 0 ) could not reproduced the magnitude of the quenching cross section dependence on the initial rotational state of OH(A 2 S + ). It was necessary to include the participation of the 1A 00 and the roto-electronic couplings between 2A 0 and 1A 00 , and 1A 0 and 1A 00 , to recover the experimental values and the rotational state dependence.…”