Co-reporter:Changjian Xie, Bin Jiang, Jacek Kłos, Praveen Kumar, Millard H. Alexander, Bill Poirier, and Hua Guo
The Journal of Physical Chemistry A July 6, 2017 Volume 121(Issue 26) pp:4930-4930
Publication Date(Web):June 14, 2017
DOI:10.1021/acs.jpca.7b04629
The fragmentation dynamics of predissociative SO2(C̃1B2) is investigated on an accurate adiabatic potential energy surface (PES) determined from high level ab initio data. This singlet PES features non-C2v equilibrium geometries for SO2, which are separated from the SO(X̃3Σ–) + O(3P) dissociation limit by a barrier resulting from a conical intersection with a repulsive singlet state. The ro-vibrational state distribution of the SO fragment is determined quantum mechanically for many predissociative states of several sulfur isotopomers of SO2. Significant rotational and vibrational excitations are found in the SO fragment. It is shown that these fragment internal state distributions are strongly dependent on the predissociative vibronic states, and the excitation typically increases with the photon energy.
Co-reporter:Marissa L. Weichman;Daniel M. Neumark;Tobias F. Sjolander;David E. Manolopoulos;Jongjin B. Kim;Jacek Kłos
Science 2015 Volume 349(Issue 6247) pp:
Publication Date(Web):
DOI:10.1126/science.aac6939
Glimpsing resonances as F and H2 react
The reaction of fluorine atoms with hydrogen molecules has long provided a window into the subtle effects of quantum mechanics on chemical dynamics. Kim et al. now show that the system still has some secrets left to reveal. The authors applied photodetachment to FH2− anions and their deuterated analogs. This allowed them to intercept the reaction trajectory in the middle and thereby uncover unanticipated weakly bound resonances. Theoretical calculations explain these observations and predict additional similar features that have yet to be seen.
Science, this issue p. 510
Co-reporter:Anyang Li, Hua Guo, Zhigang Sun, Jacek Kłos and Millard H. Alexander
Physical Chemistry Chemical Physics 2013 vol. 15(Issue 37) pp:15347-15355
Publication Date(Web):17 Jul 2013
DOI:10.1039/C3CP51870A
The state-to-state reaction dynamics of the title reaction is investigated on the ground electronic state potential energy surface using two quantum dynamical methods. The results obtained using the Chebyshev real wave packet method are in excellent agreement with those obtained using the time-independent method, except at low translational energies. It is shown that this exothermic hydrogen abstraction reaction is direct, resulting in a strong back-scattered bias in the product angular distribution. The HF product is highly excited internally. Agreement with available experimental data is only qualitative. We discuss several possible causes of disagreement with experiment.
Co-reporter:Jeffrey D. Steill, Jeffrey J. Kay, Grant Paterson, Thomas R. Sharples, Jacek Kłos, Matthew L. Costen, Kevin E. Strecker, Kenneth G. McKendrick, M. H. Alexander, and David W. Chandler
The Journal of Physical Chemistry A 2013 Volume 117(Issue 34) pp:8163-8174
Publication Date(Web):April 23, 2013
DOI:10.1021/jp402019s
We report the direct angle-resolved measurement of collision-induced alignment of short-lived electronically excited molecules using crossed atomic and molecular beams. Utilizing velocity-mapped ion imaging, we measure the alignment of NO in its first electronically excited state (A2Σ+) following single collisions with Ne atoms. We prepare A2Σ+ (v = 0, N = 0, j = 0.5) and by comparing images obtained using orthogonal linear probe laser polarizations, we experimentally determine the degree of alignment induced by collisional rotational excitation for the final rotational states N′ = 4, 5, 7, and 9. The experimental results are compared to theoretical predictions using both a simple classical hard-shell model and quantum scattering calculations on an ab initio potential energy surface (PES). The experimental results show overall trends in the scattering-angle dependent polarization sensitivity that are accounted for by the simple classical model, but structure in the scattering-angle dependence that is not. The quantum scattering calculations qualitatively reproduce this structure, and we demonstrate that the experimental measurements have the sensitivity to critique the best available potential surfaces. This sensitivity to the PES is in contrast to that predicted for ground-state NO(X) alignment.
Co-reporter:Bo Wen and Henning Meyer, Jacek Kłos and Millard H. Alexander
The Journal of Physical Chemistry A 2009 Volume 113(Issue 26) pp:7366-7375
Publication Date(Web):April 23, 2009
DOI:10.1021/jp811513j
We describe the first measurement of the near IR spectrum of the NO−Kr van der Waals complex. A variant of IR-REMPI double-resonance spectroscopy is employed in which the IR and UV lasers are scanned simultaneously in such a way that throughout the scan the sum of the two photon energies is kept constant, matching a UV resonance of the system. In the region of the first overtone vibration of the NO monomer, we observe several rotationally resolved bands for the NO−Kr complex. In addition to the origin band located at 3723.046 cm−1, we observe excited as well as hot bands involving the excitation of one or two quanta of z-axis rotation. Another band is assigned to the excitation of one quantum of bending vibration. The experimental spectra are compared with results of bound-state calculations for a new set of potential energy surfaces calculated at the spin-restricted coupled cluster level. For the average vibration−rotation energies, there is excellent agreement between the theoretical results based on the coupled states (CS) approximation and the full close-coupling (CC) treatment. Finer details like the electrostatic splitting and the P-type doubling of the rotational levels are accounted for only within the CC formalism. The comparison of the CC results with the measured spectra confirms the high quality of the PESs. However, the high resolution of the experiments is sufficient to identify some inaccuracies in the difference between the potential energy surfaces of A′ and A′′ reflection symmetry.
Co-reporter:Ani Khachatrian, Paul J. Dagdigian, Doran I. G. Bennett, François Lique, Jacek Kłos and Millard H. Alexander
The Journal of Physical Chemistry A 2009 Volume 113(Issue 16) pp:3922-3931
Publication Date(Web):February 12, 2009
DOI:10.1021/jp810148w
Optical−optical double resonance was employed to study rotational energy transfer in collisions of selected rotational/fine-structure levels of CN(A2Π, v = 3) with N2. The CN radical was generated by 193 nm photolysis of BrCN in a slow flow of N2 at total pressures of 0.2−1.4 Torr. Specific fine-structure Λ-doublet levels of CN(A2Π, v = 3) were prepared by pulsed dye laser excitation on isolated lines in the CN A−X (3,0) band, while the initially excited and collisionally populated levels were observed after a short delay by laser-induced fluorescence in the B−A (3,3) band. Total removal rate constants for specified rotational/fine-structure levels involving total angular momentum J from 4.5 to 12.5 were determined. These rate constants decrease with increasing J, with no obvious dependence on the fine-structure/Λ-doublet label. State-to-state relative rate constants were determined for several initial levels and show a strikingly strong collisional propensity to conserve the fine-structure/Λ-doublet label. Comparison is made with the results of quantum scattering calculations based on potential energy surfaces averaged over the orientation of the N2 molecule. Reasonable agreement is found with experimentally determined total removal rate constants. However, the computed state-to-state rate constants show a stronger propensity for fine-structure and Λ-doublet changing transitions. These differences between experiment and theory could be due to the neglect of the N2 orientation and the correlation of the CN and N2 angular motions.
Co-reporter:Xingan Wang;Wenrui Dong;Chunlei Xiao;Li Che;Zefeng Ren;Dongxu Dai;Xiuyan Wang;Piergiorgio Casavecchia;Xueming Yang;Bin Jiang;Daiqian Xie;Zhigang Sun;Soo-Y. Lee;Dong H. Zhang;Hans-Joachim Werner
Science 2008 Vol 322(5901) pp:573-576
Publication Date(Web):24 Oct 2008
DOI:10.1126/science.1163195
Abstract
Elementary triatomic reactions offer a compelling test of our understanding of the extent of electron-nuclear coupling in chemical reactions, which is neglected in the widely applied Born-Oppenheimer (BO) approximation. The BO approximation predicts that in reactions between chlorine (Cl) atoms and molecular hydrogen, the excited spin-orbit state (Cl*) should not participate to a notable extent. We report molecular beam experiments, based on hydrogen-atom Rydberg tagging detection, that reveal only a minor role of Cl*. These results are in excellent agreement with fully quantum-reactive scattering calculations based on two sets of ab initio potential energy surfaces. This study resolves a previous disagreement between theory and experiment and confirms our ability to simulate accurately chemical reactions on multiple potential energy surfaces.
Co-reporter:Etienne Garand;David E. Manolopoulos;Jia Zhou;Daniel M. Neumark
Science 2008 Volume 319(Issue 5859) pp:72-75
Publication Date(Web):04 Jan 2008
DOI:10.1126/science.1150602
Abstract
The degree of electronic and nuclear coupling in the Cl + H2 reaction has become a vexing problem in chemical dynamics. We report slow electron velocity-map imaging (SEVI) spectra of ClH2– and ClD2–. These spectra probe the reactant valley of the neutral reaction potential energy surface, where nonadiabatic transitions responsible for reactivity of the Cl excited spin-orbit state with H2 would occur. The SEVI spectra reveal progressions in low-frequency Cl·H2 bending and stretching modes, and are compared to simulations with and without nonadiabatic couplings between the Cl spin-orbit states. Although nonadiabatic effects are small, their inclusion improves agreement with experiment. This comparison validates the theoretical treatment, especially of the nonadiabatic effects, in this critical region of the Cl + H2 reaction, and suggests strongly that these effects are minor.
Co-reporter:Li Che;Zefeng Ren;Xingan Wang;Wenrui Dong;Dongxu Dai;Xiuyan Wang;Dong H. Zhang;Xueming Yang;Liusi Sheng;Guoliang Li;Hans-Joachim Werner;François Lique
Science 2007 Volume 317(Issue 5841) pp:1061-1064
Publication Date(Web):24 Aug 2007
DOI:10.1126/science.1144984
Abstract
The reaction of F with H2 and its isotopomers is the paradigm for an exothermic triatomic abstraction reaction. In a crossed-beam scattering experiment, we determined relative integral and differential cross sections for reaction of the ground F(2P3/2) and excited F*(2P1/2) spin-orbit states with D2 for collision energies of 0.25 to 1.2 kilocalorie/mole. At the lowest collision energy, F* is ∼1.6 times more reactive than F, although reaction of F* is forbidden within the Born-Oppenheimer (BO) approximation. As the collision energy increases, the BO-allowed reaction rapidly dominates. We found excellent agreement between multistate, quantum reactive scattering calculations and both the measured energy dependence of the F*/F reactivity ratio and the differential cross sections. This agreement confirms the fundamental understanding of the factors controlling electronic nonadiabaticity in abstraction reactions.
Co-reporter:Sule Atahan, Jacek Kłos, Piotr S. Żuchowski and Millard H. Alexander
Physical Chemistry Chemical Physics 2006 vol. 8(Issue 38) pp:4420-4426
Publication Date(Web):29 Aug 2006
DOI:10.1039/B608871F
We report an ab initio study of the van der Waals region of the O(3P)–H2 potential energy surface based on RCCSD(T) calculations with an aug-cc-pVQZ basis supplemented by bond functions. In addition, an open-shell implementation of symmetry-adapted perturbation theory (SAPT) is used to corroborate the RCCSD(T) calculations and to investigate the relative magnitudes of the various contributions to the van der Waals interaction. We also investigate the effect of the spin–orbit coupling on the position and depth of the van der Waals well. We predict the van der Waals minimum to occur in perpendicular geometry, and located at a closer distance than a secondary well in colinear geometry. The potentials obtained in the present study confirm the previous calculations of Alexander [M. H. Alexander, J. Chem. Phys., 1998, 108, 4467], but disagree with the earlier work of Harding and co-workers [Z. Li, V. A. Apkarian and L. B. Harding, J. Chem. Phys., 1997, 106, 942] as well as with recently refitted surfaces of Brandão and coworkers [J. Brandão, C. Mogo and B. C. Silva, J. Chem. Phys., 2004, 121, 8861]. Inclusion of spin–orbit coupling reduces the depth of the van der Waals minimum without causing a change in its position.
Co-reporter:Yi-Ren Tzeng and Millard Alexander
Physical Chemistry Chemical Physics 2004 vol. 6(Issue 21) pp:5018-5025
Publication Date(Web):13 Aug 2004
DOI:10.1039/B409685A
We report fully-quantum calculations of product translational energy distribution functions for the F + HD → FH + D, FD + H reactions. We include all three potential energy surfaces and all couplings (non-adiabatic, spin–orbit, and Coriolis) between them. Comparisons with the experimental results by Liu and co-workers (F. Dong, S. H. Lee and K. Liu, J. Chem. Phys., 2000, 113, 3633) confirm the relatively low reactivity of spin–orbit excited state (F*) atoms. At low collision energies formation of HF(v′
= 3) products is allowed only for reaction of F*. Once energetically allowed, the reactivity of the F ground state dominates. Excellent agreement with experiment is obtain under the assumption of an F*:F concentration ratio of 0.16:0.84 in the molecular beam, which corresponds to a thermal equilibrium of the two spin–orbit states at the experimental temperature (600 K). From the accurate calculation of the F* reactivity and its relatively small contribution to the overall reactivity of the reaction, we attribute discrepancies between calculation and experiment to an inadequacies in the simulation of the reactivity of the F ground state, likely a result of the residual errors in the ground electronic potential energy surface. In addition, we compare the predicted HF(v′
= 3) rotational distributions from reaction of F* at Ec
= 0.6 kcal mol−1 with the experimental results of Nesbitt and co-workers (W. W. Harper, S. A. Nizkorodov and D. J. Nesbitt, J. Chem. Phys., 2002, 116, 5622). Good agreement is seen.
Co-reporter:Anyang Li, Hua Guo, Zhigang Sun, Jacek Kłos and Millard H. Alexander
Physical Chemistry Chemical Physics 2013 - vol. 15(Issue 37) pp:NaN15355-15355
Publication Date(Web):2013/07/17
DOI:10.1039/C3CP51870A
The state-to-state reaction dynamics of the title reaction is investigated on the ground electronic state potential energy surface using two quantum dynamical methods. The results obtained using the Chebyshev real wave packet method are in excellent agreement with those obtained using the time-independent method, except at low translational energies. It is shown that this exothermic hydrogen abstraction reaction is direct, resulting in a strong back-scattered bias in the product angular distribution. The HF product is highly excited internally. Agreement with available experimental data is only qualitative. We discuss several possible causes of disagreement with experiment.
