Dynamics of vibrationally inelastic collisions in H+−H2: comparing quantum calculations with experiments (original) (raw)
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Physical Review A, 2002
We present a detailed quantum-mechanical study for dissociation of vibrationally excited molecular diatomic target, of H 2 ( i ) by proton impact and H 2 ϩ ( i ) by hydrogen-atom impact, in the range of center-of-mass collision energies from threshold to 9.5 eV. The dominant dissociation mechanisms in this three-atomic collision system are identified and their effectiveness analyzed for different collision geometries. The cross section calculations for direct and charge-transfer dissociation are performed by solving the Schrödinger equation for the nuclear and electronic motions on the two lowest diabatic electronic surfaces of H 3 ϩ , and by using an expansion of nuclear wave function in a vibrational basis containing all discrete H 2 and H 2 ϩ states and a large number of pseudostates from each of the corresponding discretized continua. The energy and angular spectra of the fragments are also calculated and analyzed.
The Journal of Chemical Physics, 2013
Quantum scattering calculations of vibration-vibration (VV) and vibration-translation (VT) energy transfer for non-reactive H 2 -H 2 collisions on a full-dimensional potential energy surface are reported for energies ranging from the ultracold to the thermal regime. The efficiency of VV and VT transfer is known to strongly correlate with the energy gap between the initial and final states. In H 2 (v = 1, j = 0) + H 2 (v = 0, j = 1) collisions, the inelastic cross section at low energies is dominated by a VV process leading to H 2 (v = 0, j = 0) + H 2 (v = 1, j = 1) products. At energies above the opening of the v = 1, j = 2 rotational channel, pure rotational excitation of the para-H 2 molecule leading to the formation of H 2 (v = 1, j = 2) + H 2 (v = 0, j = 1) dominates the inelastic cross section. For vibrationally excited H 2 in the v = 2 vibrational level colliding with H 2 (v = 0), the efficiency of both VV and VT process is examined. It is found that the VV process leading to the formation of 2H 2 (v = 1) molecules dominates over the VT process leading to H 2 (v = 1) + H 2 (v = 0) products, consistent with available experimental data, but in contrast to earlier semiclassical results. Overall, VV processes are found to be more efficient than VT processes, for both distinguishable and indistinguishable H 2 -H 2 collisions confirming room temperature measurements for v = 1 and v = 2.
Full-dimensional quantum dynamics calculations of H2–H2 collisions
The Journal of Chemical Physics, 2011
We report quantum dynamics calculations of rotational and vibrational energy transfer in collisions between two para-H 2 molecules over collision energies spanning from the ultracold limit to thermal energies. Results obtained using a recent full-dimensional H 2 -H 2 potential energy surface (PES) developed by Hinde [J. Chem. Phys. 128, 154308 (2008)] are compared with those derived from the Boothroyd, Martin, Keogh, and Peterson (BMKP) PES [J. Chem. Phys. 116, 666 ]. For vibrational relaxation of H 2 (v = 1, j = 0) by collisions with H 2 (v = 0, j = 0) as well as rotational excitations in collisions between ground state H 2 molecules, the PES of Hinde is found to yield results in better agreement with available experimental data. A highly efficient near-resonant energy transfer mechanism that conserves internal rotational angular momentum and was identified in our previous study of the H 2 -H 2 system [Phys. Rev. A 77, 030704(R) (2008)] using the BMKP PES is also found to be reproduced by the Hinde PES, demonstrating that the process is largely insensitive to the details of the PES. In the absence of the near-resonance mechanism, vibrational relaxation is driven by the anisotropy of the potential energy surface. Based on a comparison of results obtained using the Hinde and BMKP PESs with available experimental data, it appears that the Hinde PES provides a more accurate description of rotational and vibrational transitions in H 2 -H 2 collisions, at least for vibrational quantum numbers v ≤ 1.
Vibrational Excitation ofH2by Proton Impact
Physical Review A
The forward-scattered component of the absolute cross sections for protonand deuteronimpact excitation of the first four vibrational levels of the electronic ground state of H2 have been measured. Excitation cross-section measurements are reported for laboratory energies from 100 to 1500 eV; and, for energies below 100 eV, excitation cross sections are reported for forward-scattered protons from 8=0' to 8=1.9'. The cross sections were measured from the peak intensities observed in the ion energy-loss spectra generated by passing a highquality proton beam (energy spread & 80 meV, angular divergence-+ 1') through a collision chamber containing the target gas at room temperature. Each excitation cross section (crp"i, where the quantum number v' refers to the final energy level) is found to reach a maximum value at an energy which decreases with increasing quantum number 'p': opl(max) = 1.37x 10 " cm at 200 eV, op2(max) =0. 342 x10 cm at140 eV, ando. p3(max) =0.078 && 10~" cm andg. p4(max) =0. 021x10 ' cm both at 110 eV. These maxima give collision times and distances which are consistent with the adiabatic hypothesis. For energies beyond the maxima, the cross sections decrease very slowly with increasing energy. Furthermore, the cross sections for excitation to the higher levels decrease more rapidly than the cross sections for excitation to the lower levels, an effect predicted by Shin in a three-dimensional calculation involving a semiclassical theory for the excitation of a classical harmonic oscillator. A comparison of our results with vibrational excitation studies of other systems demonstrates the unique features of the H'-H& system. The large values of these vibrational excitation cross sections and their wide effective kinetic energy span show that vibrational excitation must be an important process in a wide variety of physical phenomena.
Journal of Molecular Structure: THEOCHEM, 2001
We report a systematic study on the role played by electronic correlation of target on vibrational excitation processes of molecules by electron impact. More speci®cally, cross sections for vibrationally elastic and inelastic electron±H 2 collisions are reported in the 1.5±40 eV range. In our study, the electron±molecule interaction potential is derived using both the near-Hartree±Fock and the con®guration interaction target wavefunctions. The body-frame vibrational close-coupling equations are solved using the method of continued fractions (MCF). Our study has shown that the MCF is a very ef®cient method for solving such scattering equations. In addition, the calculated results have shown that the electronic correlation effects of target signi®cantly in¯uence the calculated vibrational excitation cross sections at low incident energies and for the excitations leading to high-lying vibrational levels. Nevertheless, these effects are not relevant at higher incident energies.
Exact exchange effects on vibrational excitation of H 2 by electron impact
A representation of the exact nonlocal exchange-potential operator is proposed and applied to study electronimpact vibrational excitation of H 2 in the low-and intermediate-energy range. In our approach, a complete set of one-dimensional particle-in-box wave functions is used as expansion basis. This representation of the exchange operator is easy to program and the calculated cross sections converge rapidly with the number of basis functions. Excitation cross sections for the transitions vЈϭ0→vϭ0, 1, 2, and 3 calculated in the 1.5-100-eV range are in general good agreement with the available experimental and theoretical data.
Physical chemistry chemical physics : PCCP, 2016
State-to-state cross-sections for the S(+) + H2(v,j) → SH(+)(v',j') + H endothermic reaction are obtained using quantum wave packet (WP) and quasi-classical (QCT) methods for different initial ro-vibrational H2(v,j) over a wide range of translation energies. The final state distribution as a function of the initial quantum number is obtained and discussed. Additionally, the effect of the internal excitation of H2 on the reactivity is carefully studied. It appears that energy transfer among modes is very inefficient that vibrational energy is the most favorable for the reaction, and rotational excitation significantly enhances the reactivity when vibrational energy is sufficient to reach the product. Special attention is also paid to an unusual discrepancy between classical and quantum dynamics for low rotational levels while agreement improves with rotational excitation of H2. An interesting resonant behaviour found in WP calculations is also discussed and associated with th...
Benchmark calculations of electron impact electronic excitation of the hydrogen molecule
Journal of Physics B: Atomic, Molecular and Optical Physics, 2020
We present benchmark integrated and differential cross-sections for electron collisions with H2 using two different theoretical approaches, namely, the R-matrix and molecular convergent close-coupling. This is similar to comparative studies conducted on electron–atom collisions for H, He and Mg. Electron impact excitation to the b 3 Σ u + , a 3 Σ g + , B 1 Σ u + , c3Πu, E F 1 Σ g + , C1Πu, e 3 Σ u + , h 3 Σ g + , B ′ 1 Σ u + and d3Πu excited electronic states are considered. Calculations are presented in both the fixed nuclei and adiabatic nuclei approximations, where the latter is shown only for the b 3 Σ u + state. Good agreement is found for all transitions presented. Where available, we compare with existing experimental and recommended data.
The Journal of Chemical Physics, 2014
Collision-induced energy transfer involving H 2 molecules plays an important role in many areas of physics. Kinetic models often require a complete set of state-to-state rate coefficients for H 2 +H 2 collisions in order to interpret results from spectroscopic observations or to make quantitative predictions. Recent progress in full-dimensional quantum dynamics using the numerically exact closecoupling (CC) formulation has provided good agreement with existing experimental data for lowlying states of H 2 and increased the number of state-to-state cross sections that may be reliably determined over a broad range of energies. Nevertheless, there exist many possible initial states (e.g., states with high rotational excitation) that still remain elusive from a computational standpoint even at relatively low collision energies. In these cases, the coupled-states (CS) approximation offers an alternative full-dimensional formulation. We assess the accuracy of the CS approximation for H 2 +H 2 collisions by comparison with benchmark results obtained using the CC formulation. The results are used to provide insight into the orientation effects of the various internal energy transfer mechanisms. A statistical CS approximation is also investigated and cross sections are reported for transitions which would otherwise be impractical to compute. © 2014 AIP Publishing LLC. [http://dx.