Observation of the geometric phase effect in the H + HD → H2+ D reaction

Science ◽  
2018 ◽  
Vol 362 (6420) ◽  
pp. 1289-1293 ◽  
Author(s):  
Daofu Yuan ◽  
Yafu Guan ◽  
Wentao Chen ◽  
Hailin Zhao ◽  
Shengrui Yu ◽  
...  
Keyword(s):  
Cross Sections ◽  
Geometric Phase ◽  
Potential Energy Surfaces ◽  
Molecular Beams ◽  
Conical Intersection ◽  
Molecular Systems ◽  
Quantum State Resolved ◽  
State Potential ◽  
Energy Surfaces ◽  
Angular Oscillations

Theory has established the importance of geometric phase (GP) effects in the adiabatic dynamics of molecular systems with a conical intersection connecting the ground- and excited-state potential energy surfaces, but direct observation of their manifestation in chemical reactions remains a major challenge. Here, we report a high-resolution crossed molecular beams study of the H + HD → H2+ D reaction at a collision energy slightly above the conical intersection. Velocity map ion imaging revealed fast angular oscillations in product quantum state–resolved differential cross sections in the forward scattering direction for H2products at specific rovibrational levels. The experimental results agree with adiabatic quantum dynamical calculations only when the GP effect is included.

scholarly journals New H2O–H2O collisional rate coefficients for cometary applications

2020 ◽  
Vol 498 (4) ◽  
pp. 5489-5497 ◽  
Author(s):  
C Boursier ◽  
B Mandal ◽  
D Babikov ◽  
M L Dubernet
Keyword(s):  
Cross Sections ◽  
Potential Energy Surfaces ◽  
Rate Coefficients ◽  
Molecular Systems ◽  
Large Sets ◽  
Alternative Approach ◽  
Collisional Rate Coefficients ◽  
Energy Surfaces ◽  
Good Agreement

ABSTRACT We re-introduce a semiclassical methodology based on theories developed for the determination of broadening coefficients. We show that this simple and extremely fast methodology provides results that are in good agreement with results obtained using the more sophisticate MQCT approach. This semiclassical methodology could be an alternative approach which allows to provide large sets of collisional data for very complex molecular systems. It saves time both on the determination of potential energy surfaces and on the collisional dynamical calculations. In addition, this paper provides more complete sets of rotational de-excitation cross-sections and rate coefficients of H2O perturbed by a thermal average of water molecules. Those data can be used in the radiative transfer modelling of cometary atmospheres.

scholarly journals Geometric Phase Effects in Ultracold Chemical Reactions

Atoms ◽  
2019 ◽  
Vol 7 (3) ◽  
pp. 65 ◽  
Author(s):  
Brian Kendrick ◽  
N. Balakrishnan
Keyword(s):  
Geometric Phase ◽  
Potential Energy Surfaces ◽  
Hydrogen Exchange ◽  
Decisive Role ◽  
Conical Intersection ◽  
Chemical Dynamics ◽  
Phase Effect ◽  
Theoretical Investigations ◽  
Energy Surfaces

The role of the geometric phase effect in chemical reaction dynamics has long been a topic of active experimental and theoretical investigations. The topic has received renewed interest in recent years in cold and ultracold chemistry where it was shown to play a decisive role in state-to-state chemical dynamics. We provide a brief review of these developments focusing on recent studies of O + OH and hydrogen exchange in the H + H 2 and D + HD reactions at cold and ultracold temperatures. Non-adiabatic effects in ultracold chemical dynamics arising from the conical intersection between two electronic potential energy surfaces are also briefly discussed. By taking the hydrogen exchange reaction as an illustrative example it is shown that the inclusion of the geometric phase effect captures the essential features of non-adiabatic dynamics at collision energies below the conical intersection.

scholarly journals X-ray emission spectroscopy: a genetic algorithm to disentangle core–hole-induced dynamics

2021 ◽  
Vol 140 (12) ◽  
Author(s):  
Lars G. M. Pettersson ◽  
Osamu Takahashi
Keyword(s):  
Genetic Algorithm ◽  
Cross Sections ◽  
Potential Energy Surfaces ◽  
Water Clusters ◽  
Life Time ◽  
Core Hole ◽  
Final State ◽  
X Ray ◽  
State Potential ◽  
Energy Surfaces

AbstractA genetic algorithm (GA) is developed and applied to make proper connections of final-state potential-energy surfaces and X-ray emission (XES) cross sections between steps in the time-propagation of H-bonded systems after a core–hole is created. We show that this modification results in significantly improved resolution of spectral features in XES with the semiclassical Kramers–Heisenberg approach which takes into account important interference effects. We demonstrate the effects on a water pentamer model as well as on two 17-molecules water clusters representing, respectively, tetrahedral (D2A2) and asymmetric (D1A1) H-bonding environments. For D2A2, the applied procedure improves significantly the obtained intensities, whereas for D1A1 the effects are smaller due to milder dynamics during the core–hole life-time as only one hydrogen is involved. We reinvestigate XES for liquid ethanol and, by properly disentangling the relevant states in the dense manifold of states using the GA, now resolve the important 3a′′ state as a peak rather than a shoulder. Furthermore, by applying the SpecSwap-RMC procedure, we reweigh the distribution of structures in the sampling of the liquid to fit to experiment and estimate the ratio between the main anti and gauche conformers in the liquid at room temperature. This combination of techniques will be generally applicable to challenging problems in liquid-phase spectroscopy.

scholarly journals Potential Energy Surfaces for Unsaturated Hydrocarbons from Crossed Molecular Beams

1997 ◽  
Vol 50 (3) ◽  
pp. 683
Author(s):  
K. P. Stevenson ◽  
J. D. Close ◽  
P. L. Muiño ◽  
R. O. Watts
Keyword(s):  
Potential Energy ◽  
Cross Sections ◽  
Potential Energy Surfaces ◽  
Interaction Strength ◽  
Molecular Beams ◽  
Unsaturated Hydrocarbon ◽  
Atmospheric Gases ◽  
Weakly Bound ◽  
Energy Surfaces ◽  
Scattering Cross Sections

The total differential scattering cross sections for several important unsaturated hydrocarbon molecules with common atmospheric gases were measured in a crossed molecular beam apparatus. The experiments show quantum interferences which relate to potential energy surface parameters, such as the well depth and radial minimum. The damping of the quantum features, over contributions from experimental resolutions, provides information on the angular and radial anisotropies present in the potential energy surfaces. We have investigated two areas: (1) the role of the probe partner in determining the interaction strength for a given hydrocarbon target, and (2) the effect of increasing the overall length of the hydrocarbon molecule for a fixed probe. By comparing results for a class of scattering systems, we can identify chemical and physical trends that determine the van der Waals potential energy surfaces of larger molecules. We expect these results to aid in the prediction and interpretation of complementary experimental measurements on the high resolution infrared spectroscopy of weakly bound complexes.

Resolving the Quadruple Bonding Conundrum in C2 Using Insights Derived from Excited State Potential Energy Surfaces: A Molecular Orbital Perspective

2019 ◽  
Author(s):  
Ishita Bhattacharjee ◽  
Debashree Ghosh ◽  
Ankan Paul
Keyword(s):  
Excited State ◽  
Potential Energy ◽  
Molecular Orbital ◽  
High Spin ◽  
Potential Energy Surfaces ◽  
Valence Bond ◽  
Deep Minimum ◽  
State Potential ◽  
Energy Surfaces ◽  
Mo Theory

The question of quadruple bonding in C<sub>2</sub> has emerged as a hot button issue, with opinions sharply divided between the practitioners of Valence Bond (VB) and Molecular Orbital (MO) theory. Here, we have systematically studied the Potential Energy Curves (PECs) of low lying high spin sigma states of C<sub>2</sub>, N<sub>2</sub> and Be<sub>2</sub> and HC≡CH using several MO based techniques such as CASSCF, RASSCF and MRCI. The analyses of the PECs for the<sup> 2S+1</sup>Σ<sub>g/u</sub> (with 2S+1=1,3,5,7,9) states of C<sub>2</sub> and comparisons with those of relevant dimers and the respective wavefunctions were conducted. We contend that unlike in the case of N<sub>2</sub> and HC≡CH, the presence of a deep minimum in the <sup>7</sup>Σ state of C<sub>2</sub> and CN<sup>+</sup> suggest a latent quadruple bonding nature in these two dimers. Hence, we have struck a reconciliatory note between the MO and VB approaches. The evidence provided by us can be experimentally verified, thus providing the window so that the narrative can move beyond theoretical conjectures.

scholarly journals Ultraviolet spectroscopy of pressurized and supercritical carbon dioxide

2021 ◽  
Vol 4 (1) ◽  
Author(s):  
Timothy W. Marin ◽  
Ireneusz Janik
Keyword(s):  
Carbon Dioxide ◽  
Potential Energy Surfaces ◽  
Vacuum Ultraviolet ◽  
Electronic Absorption Spectra ◽  
Industrial Applications ◽  
Ultraviolet Spectroscopy ◽  
Collisional Broadening ◽  
Thermodynamic Critical Point ◽  
State Potential ◽  
Energy Surfaces

AbstractCarbon dioxide (CO2) is prevalent in planetary atmospheres and sees use in a variety of industrial applications. Despite its ubiquitous nature, its photochemistry remains poorly understood. In this work we explore the density dependence of pressurized and supercritical CO2 electronic absorption spectra by vacuum ultraviolet spectroscopy over the wavelength range 1455-2000 Å. We show that the lowest absorption band transition energy is unaffected by a density increase up to and beyond the thermodynamic critical point (137 bar, 308 K). However, the diffuse vibrational structure inherent to the spectrum gradually decreases in magnitude. This effect cannot be explained solely by collisional broadening and/or dimerization. We suggest that at high densities close proximity of neighboring CO2 molecules with a variety of orientations perturbs the multiple monomer electronic state potential energy surfaces, facilitating coupling between binding and dissociative states. We estimate a critical radius of ~4.1 Å necessary to cause such perturbations.

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