Renner–Teller induced predissociation of HNO(Ã 1A″): Rotational-state dependent linewidths of quasibound states

Abstract

The electronic spectrum of the fluoroborane free radical. II. Analysis of laser-induced fluorescence and single vibronic level emission spectra Extremely narrow peaks in predissociation of sodium dimer due to rovibronic couplingThe predissociation dynamics in the à 1 AЉ electronic state of HNO is investigated. The quantum mechanical dynamics calculations take into account the Renner-Teller ͑or electronic Coriolis͒ coupling with the electronic ground state X 1 AЈ, which appears to be the dominant decay mechanism for the quasi-bound vibrational states in the à 1 AЉ upper state. All three internal vibrational degrees of freedom are incorporated and two ab initio potential energy surfaces are used. The linewidths, ⌫, are directly calculated by the filter diagonalization method and an absorbing optical potential in the exit channel. They are generally small (ϳ1 cm Ϫ1 ) and increase with excitation of the bending mode ͑bent-to-bent transition͒. On average, ⌫ increases with K, the a-axis rotational quantum number. However, for some vibrational states the linewidth shows a non-monotonic behavior with K, which is the result of mixing with highly excited vibrational levels in the continuum of the ground electronic state. This effect is even more striking, when the total angular momentum quantum number J is varied: In some cases, the linewidth exhibits a pronounced resonancelike behavior as function of J. The agreement with recent experimental spectroscopic data is satisfactory. The calculated linewidths are of the same order ͑within a factor of 2 or so͒ as the experimental ones. However, because the two ab initio potential energy surfaces do not reproduce sufficiently well the X -à excitation energies, the resonancelike effects are not quantitatively described. Potential energy surfaces with considerably higher accuracy are required.

The unimolecular dissociation of HCO. V. Mixings between resonance states

“…4 for different values of J and K. They are in essence similar to the calculations described by Weiss et al 6,12 for the Renner-Teller induced dissociations of HCO and HNO, re-spectively, with the exception that only one electronic state, that is the ground state, is included. In short, we use the filter diagonalization ͑FD͒ method [13][14][15] and an imaginary potential in the exit channel in order to absorb the wave function at the edge of the grid.…”

“…In view of the recent experimental 7,8 and theoretical 9,10 studies of HOCl in the ground state as well as recent calculations for the predissociation of HNO(Ã ) via Renner-Teller coupling to the ground electronic state, 6 it appears very likely that the resonancelike structures are caused by the systematic mixing of the (0,v 2 ,1) states with other nearby vibrational states. These perturbing or ''doorway'' states belong to another progression whose widths must be considerably larger than the widths of the (0,v 2 ,1) progression.…”

Spin-orbit mechanism of predissociation in the Wulf band of ozone

“…Fluctuations are often fingerprints of "dark" states which are accidentally degenerate with the "bright" level. Variation of the angular momentum shifts resonances of different electronic states through each other 23 with the effect that the "doorway states" for J = 0 and J Ͼ 0 may be different.…”

Quantum Mechanical Studies of Photodissociation Dynamics Using Accurate Global Potential Energy Surfaces

“…In this case, the probability to penetrate into the linear regime is relatively small, the RT coupling is weak, and consequently the lifetime is long. 113 In contrast to HCO, bending excitation increases the RT coupling and therefore decreases the lifetime.…”

“…113 In order to quantitatively reproduce these effects, the PESs of the ground and the excited state must be extremely accurate and the vertical separation between them must also be precise. The mixing between resonances and the tuning of the resonance via rotational excitation, for example, is a generic effect, when two electronic states are coupled, irrespective of the nature of the coupling.…”