Nonadiabatic quantum wave packet dynamics of the H + H<SUB>2</SUB> reaction including the coriolis coupling

The effect of coriolis coupling on the dynamics of H + H2 reaction is examined by calculating the initial state-selected and energy resolved reaction probabilities on the coupled manifold of its degenerate 2p (E') ground electronic state. H3 in this state is prone to the Jahn-Teller (JT) instability and consequently the degeneracy is split upon distortion from its D3h equilibrium geometry. The orbital degeneracy is, however, restored along the D3h symmetry configuration and it results into conical intersections of the two JT split component states. The energetically lower adiabatic component of latter is repulsive, and mainly ('rather solely') drive the H + H2 reaction dynamics. On the otherhand, the upper adiabatic component is of bound type and can only impart non-adiabaticity on the dynamics of lower state. Comparison calculations are therefore also carried out on the uncoupled lower adiabatic sheet to assess the nonadiabatic effect. Exact quantum scattering calculations are performed by a chebyshev polynomial propagator and employing the double many body expansion potential energy surface of the electronic ground state of H3. Reaction probabilities are reported up to a total energy of &#8764;3.0 eV, slightly above the energetic minimum of the seam of conical intersections at &#8764;2.74 eV. Reaction probabilities are calculated up to the total angular momentum, J = 20 and for each value of J, the projection quantum number K is varied from 0 to min (J, Kmax), with Kmax = 4. Probability results are compared and discussed with those obtained without the coriolis coupling

Reactive chemical dynamics through conical intersections

Reaction dynamics of prototypical, D + H2 and Cl (2P) + H2, chemical reactions occurring through the conical intersections of the respective coupled multi-sheeted potential energy surfaces is examined here. In addition to the electronic coupling, nonadiabatic effects due to relativistic spin-orbit coupling are also considered for the latter reaction. A time-dependent wave packet propagation approach is undertaken and the quantum dynamical observables viz., energy resolved reaction probabilities, integral reaction cross-sections and thermal rate constants are reported

Quantum wave packet dynamics of N(²D) + H₂ reaction

The quantum wave packet dynamics of the title reaction within the coupled state approximation is examined here and initial state-selected reaction probabilities, integral reaction cross sections, and thermal rate constants are reported. The ab initio potential energy surface of the electronic ground state (1²A^") of the system recently reported by Ho et al. [J. Chem. Phys.,119, 3063 (2003)] is employed in this investigation. All partial wave contributions up to the total angular momentum J=55 were necessary to obtain converged integral reaction cross sections up to a collision energy of 1.0 eV. Thermal rate constants are calculated from the reaction cross sections and compared with the available theoretical and experimental results. Typical resonances formed during the course of the reaction and elucidating the insertion type mechanism for the product formation are calculated. Vibrational energy levels supported by the deep well (∼5.5eV) of the 1²A^" potential energy surface of NH₂ are also calculated for the total angular momentum J=0. A statistical analysis of the spacing between the adjacent levels of this energy spectrum is performed and the extent of irregularity in the spectral sequence is assessed

Three-beam double stimulated Raman scatterings: Cascading configuration

Two-beam stimulated Raman scattering (SRS) has been used in diverse label-free spectroscopy and imaging applications of live cells, biological tissues, and functional materials. Recently, we developed a theoretical framework for the three-beam double SRS processes that involve pump, Stokes, and depletion beams, where the pump-Stokes and pump-depletion SRS processes compete with each other. It was shown that the net Stokes gain signal can be suppressed by increasing the depletion beam intensity. The theoretical prediction has been experimentally confirmed recently. In the previous scheme for a selective suppression of one SRS by making it compete with another SRS, the two SRS processes occur in a parallel manner. However, there is another possibility of three-beam double SRS scheme that can be of use to suppress either Raman gain of the Stokes beam or Raman loss of the pump beam by depleting the Stokes photons with yet another SRS process induced by the pair of Stokes and another (second) Stokes beam. This three-beam double SRS process resembles a cascading energy transfer process from the pump beam to the first Stokes beam (SRS-1) and subsequently from the first Stokes beam to the second Stokes beam (SRS-2). Here, the two stimulated Raman gain-loss processes are associated with two different Raman-active vibrational modes of solute molecule. In the present theory, both the radiation and the molecules are treated quantum mechanically. We then show that the cascading-type three-beam double SRS can be described by coupled differential equations for the photon numbers of the pump and Stokes beams. From the approximate solutions as well as exact numerical calculation results for the coupled differential equations, a possibility of efficiently suppressing the stimulated Raman loss of the pump beam by increasing the second Stokes beam intensity is shown and discussed. To further prove a potential use of this scheme for developing a super-resolution SRS microscopy, we present a theoretical expression and numerical simulation results for the full-width-at-half-maximum of SRS imaging point spread function, assuming that the pump and Stokes beam profiles are Gaussian and the second Stokes beam has a doughnut-shaped spatial profile. It is clear that the spatial resolution with the present 3-beam cascading SRS method can be enhanced well beyond the diffraction limit. We anticipate that the present work will provide a theoretical framework for a super-resolution stimulated Raman scattering microscopy that is currently under investigation. © 2018 Author(s)1

Quantum nonadiabatic dynamics of hydrogen exchange reactions

In continuation of our earlier effort to understand the nonadiabatic coupling effects in the prototypical H + H₂ exchange reaction [Jayachander Rao et al. Chem. Phys. 333 (2007) 135], we present here further quantum dynamical investigations on its isotopic variants. The present work also corrects a technical scaling error occurred in our previous studies on the H + HD reaction. Initial state-selected total reaction cross sections and Boltzmann averaged thermal rate constants are calculated with the aid of a time-dependent wave packet approach employing the double many body expansion potential energy surfaces of the system. The theoretical results are compared with the experimental and other theoretical data whenever available. The results re-establish our earlier conclusion, on a more general perspective, that the electronic nonadiabatic effects are negligible on the important quantum dynamical observables of these reactive systems reported here

Nonadiabatic quantum wave packet dynamics of H+H₂ (HD) reactions

Initial state-selected and energy resolved integral reaction cross sections and thermal rate constants of H+H₂ and H+HD reactions are calculated on the conically intersecting ground electronic manifold. The effect of the associated nonadiabatic coupling on these dynamical quantities is examined for energies upto the three-body dissociation limit well beyond the energetic minimum of the seam of conical intersections. The quantum dynamical simulations in the coupled electronic manifold are carried out within the coupled state approximation by a time-dependent wave packet propagation method employing the double many body expansion (DBME) potential energy surface (PES) of Varandas et al. [A.J.C. Varandas, F.B. Brown, C.A. Mead, D.G. Truhlar, N.C. Blais, J. Chem. Phys. 86 (1987) 6258]. All partial wave contributions upto the total angular momentum J=50, in case of H+H₂ and J=60, in case of H+HD reactions are considered to obtain converged reaction cross sections upto a total energy of ∼4.7eV. Channel specific reaction cross sections are reported for the H+HD reaction. Analysis of the reaction probabilities for individual J values reveal no significant effect of nonadiabatic coupling on them at energies above the minimum of the seam of conical intersections occurring at ∼2.74eV. The differences observed in the reaction probability results in the uncoupled and coupled surface situation however, cancel out in the integral reaction cross sections and thermal rate constants. These findings are consistent with the recent studies on these reactions including the geometric phase change

On the (E&#8855;e)- Jahn-Teller conical intersections in the 3p(Eʹ) and 3d(E") Rydberg electronic states of triatomic hydrogen

The static and dynamic aspects of the Jahn-Teller(JT) interactions in the 3p(E′) and 3d(E")Rydberg electronic states of H3 are analyzed theoretically. The static aspects are discussed based on recent ab initio quantum chemistry results, and the dynamic aspects are examined in terms of the vibronic spectra and nonradiative decay behavior of these states. The adiabatic potential-energysurfaces of these degenerate electronic states are derived from extensive ab initio calculations. The calculated adiabatic potential-energysurfaces are diabatized following our earlier study on this system in its 2p(E′)ground electronic state. The nuclear dynamics on the resulting conically intersecting manifold of electronic states is studied by a time-dependent wave-packet approach. Calculations are performed both for the uncoupled and coupled state situations in order to understand the importance of nonadiabatic interactions due to the JT conical intersections in these excited Rydberg electronic states

Selective suppression of CARS signal with three-beam competing stimulated Raman scattering processes

Coherent Raman scattering spectroscopy and microscopy are useful methods for studying the chemical and biological structures of molecules with Raman-active modes. In particular, coherent anti-Stokes Raman scattering (CARS) microscopy, which is a label-free method capable of imaging structures by displaying the vibrational contrast of the molecules, has been widely used. However, the lack of a technique for switching-off the CARS signal has prevented the development of the super-resolution Raman imaging method. Here, we demonstrate that a selective suppression of the CARS signal is possible by using a three-beam double stimulated Raman scattering (SRS) scheme; the three beams are the pump, Stokes, and depletion lights in order of frequency. Both pump–Stokes and pump–depletion beam pairs can generate SRS processes by tuning their beat frequencies to match two different vibrational modes, then two CARS signals induced by pump–Stokes–pump and pump–depletion–pump interactions can be generated, where the two CARS signals are coupled with each other because they both involve interactions with the common pump beam. Herein, we show that as the intensity of the depletion beam is increased, one can selectively suppress the pump–Stokes–pump CARS signal because the pump–depletion SRS depletes the pump photons. A detailed theoretical description of the coupled differential equations for the three incident fields and the generated CARS signal fields is presented. Taking benzene as a molecular system, we obtained a maximum CARS suppression efficiency of about 97% with our experimental scheme, where the ring breathing mode of the benzene is associated with pump–Stokes–pump CARS, while the C–H stretching mode is associated with the competing pump–depletion SRS process. We anticipate that this selective switching-off scheme will be of use in developing super-resolution label-free CARS microscopy.©the Owner Societies 201

Probing avoided crossings and conical intersections by two-pulse femtosecond stimulated Raman spectroscopy:Theoretical study

This study leverages two-pulse femtosecond stimulated Raman spectroscopy (2FSRS) to characterize molecular systems with avoided crossings (ACs) and conical intersections (CIs) in their low-lying excited electronic states. By simulating 2FSRS spectra of microscopically inspired ACs and CIs models, we demonstrate that 2FSRS not only delivers valuable information on the molecular parameters characterizing ACs and CIs but also helps distinguish between these two systems.</p