Present Potential Energy Surface Research Articles

Dynamics of C<sup>+</sup> + H<sub>2</sub> reaction based on a new potential energy surface

The multi-reference interaction method is explicitly dependent on the electron-electron distance, and ACVQZ basis set is used in the <i>ab initio</i> calculation. The potential energy surface (PES) is fitted by using the permutation invariant polynomial neural network method based on 18222 <i>ab initio</i> points. In addition, the topographical features of the PES are compared with available theoretical and experimental data. The results indicate that the present PES is more accurate and can be applied to any type of dynamic study. In order to validate the PES, the dynamic study of the C<sup>+</sup> + H<sub>2</sub> → H + CH<sup>+</sup> reaction is carried out by using the quasi-classical trajectory method in a collision energy range of 0.4–1.0 eV. The integral cross sections and differential cross sections are calculated and compared with previous theoretical studies. For the integral cross section, the present results are, in general, in good agreement with previous theoretical studies, both of which increase with collision energy increasing. The forward and backward symmetric differential cross sections indicate that the “complex-forming” mechanism plays a dominant role in the reaction.

Collisional Quantum Dynamics for MgH- (1Σ+) With He as a Buffer Gas: Ionic State-Changing Reactions in Cold Traps.

We present in this paper a detailed theoretical and computational analysis of the quantum inelastic dynamics involving the lower rotational levels of the MgH− (X1Σ+) molecular anion in collision with He atoms which provide the buffer gas in a cold trap. The interaction potential between the molecular partner and the He (1S) gaseous atoms is obtained from accurate quantum chemical calculations at the post-Hartree-Fock level as described in this paper. The spatial features and the interaction strength of the present potential energy surface (PES) are analyzed in detail and in comparison with similar, earlier results involving the MgH+ (1Σ) cation interacting with He atoms. The quantum, multichannel dynamics is then carried out using the newly obtained PES and the final inelastic rats constants, over the range of temperatures which are expected to be present in a cold ion trap experiment, are obtained to generate the multichannel kinetics of population changes observed for the molecular ion during the collisional cooling process. The rotational populations finally achieved at specific temperatures are linked to state-selective laser photo-detachment experiments to be carried out in our laboratory.All intermediate steps of the quantum modeling are also compared with the behavior of the corresponding MgH+ cation in the trap and the marked differences which exist between the collisional dynamics of the two systems are dicussed and explained. The feasibility of the present anion to be involved in state-selective photo-detachment experiments is fully analyzed and suggestions are made for the best performing conditions to be selected during trap experiments.

Regularity in highly excited vibrational dynamics of NOCl (X 1A′): Quantum mechanical calculations on a new potential energy surface

A new potential energy surface (PES) of NOCl in the ground electronic state (X 1A′) is constructed based on multireference configuration interaction calculations. Almost all the vibrational eigenstates up to the dissociation threshold are obtained using filter diagonalization method with the present PES. The vibrational excitation energies are in good agreement with the experimental values. The nearest neighbor level spacing distribution shows that the vibrational structure is regarded as regular up to the dissociation threshold. The distribution of radiative coupling elements also supports the regularity. It is further found out that the NO stretching mode is strongly decoupled from the other modes. Taking advantage of this result, the two-dimensional (2D) analyses are carried out with the NO distance fixed. The 2D wave functions have clear nodal patterns even near the dissociation threshold, indicating that the 2D quantum dynamics is regular as in the three-dimensional case. Comparing the 2D classical dynamics with the 2D wave functions, quasiperiodic trajectories closely related to the corresponding quantum dynamics are extracted. Although it is generally believed that the phase space becomes fully chaotic with approaching to the dissociation threshold, two stable islands of regular motion still remain even at this energy region.

Quasi-classical trajectory calculations on a fast analytic potential energy surface for the [formula omitted] reaction

Quasi-classical trajectory (QCT) calculations have been carried out on a new implementation of the first singlet state a ̃ 1 A ′ potential energy surface (PES) of the C( 1 D)+ H 2 system based on a set of 1748 ab initio points previously reported. The implementation is performed by using the Reproducing Kernel Hilbert Space (RKHS) interpolation method, which allows the fast evaluation of the PES values and, particularly, their gradients analytically. Although there is a general good correspondence between the present surface and the previous version, the new PES is free of spurious small scale features and permits a faster evaluation of the PES and its gradients. The QCT results on the present PES are in general good agreement with those obtain on the previous PES.

Millimeter-wave spectroscopy of the internal-rotation band of the He–HCN complex and the intermolecular potential energy surface

Millimeter-wave absorption spectroscopy combined with a pulsed-jet expansion technique was applied to measure the internal-rotation band of He–HCN in the frequency region of 95–125 GHz. In total 13 rovibrational lines, split into nitrogen nuclear hyperfine structure, were observed for the fundamental internal-rotation band, j=1−0. The observed transition frequencies were analyzed including their hyperfine splitting to yield an intermolecular potential energy surface, as improved from the one given by a coupled-cluster single double (triple) ab initio calculation. The surface obtained has a global minimum in the linear configuration (He⋅⋅⋅H–C–N) with a well depth of 30.2 cm−1, and a saddle point located in the antilinear configuration (H–C–N⋅⋅⋅He) which is higher by 8.91 cm−1 in energy than the global minimum. The distance Rm between the He atom and the center of mass of HCN along the minimum energy path shows a strong angular dependence; Rm is 4.169 and 4.040 Å in the linear and antilinear forms, respectively, while it is 3.528 Å in a T-shaped configuration. In the first excited internal-rotation state (j=1), levels with l less than 4 are bound but not for the one with l = 5, according to the energy level diagram calculated from the present potential energy surface, where l denotes the quantum number for the end-over-end rotation of the complex. The energy level diagram is consistent with the millimeter-wave observation, in which the Δl=0 transitions with l=0∼4 were observed but not for those with l equal to or greater than 5. The band origin of the internal-rotation band, 98.70 GHz, as defined to be the same as the frequency of the R(0) transition, is larger by 11% than the J=1−0 rotational transition frequency of the free HCN molecule.

Potential energy surface for unimolecular dissociations and rearrangements of the ground state of [C2H3FO] systems

The potential energy surface (PES) of [C2H3FO] systems in its electronic ground state has been investigated using density functional theory method, at the B3LYP/6-311++G(d,p) level. Ten stable intermediates, including acetyl fluoride (1), fluoroacetaldehyde (9), 1-fluorovinyl alcohol (4), 2-fluorovinyl alcohol, carbenes and fluorooxiranes, have been located. Most stationary points on the PES corresponding to the molecular elimination and rearrangement channels from these intermediates have been identified. Ketene (8) is found to be the predominant product in the unimolecular dissociations of 1, 4, 9 and fluorooxirane (6). The most probable channels for ketene formation from acetyl fluoride are 1→8 and 1→4→8. In the reactions of both CH3CO and F radicals, both these processes are energetically feasible for the thermal reactants and hence should lead to a spontaneous emission of vibrationally hot HF. The present PES characterises the CH3CO+F reaction to be a capture-limited association–elimination reaction with a very high and pressure-independent rate coefficient. In addition to its direct decomposition to ketene, 9 can give rise to stable rearrangement products, viz., 2-fluorovinyl alcohol (12) and 6. Fluorooxirane (6) decomposes to ketene through its isomerisation to 9 as intermediate and the present study provides an explanation for the non-observation of this intermediate.

Rovibrational energy levels and transitions for H3 + computed from a new highly accurate potential energy surface

Bound rovibrational levels and selected transitions have been calculated for H3 + using a new potential energy surface (PES) computed by the CISD-R12-method. The present PES has an error of approximately 1 cm-1 in the relevant region around the minimum. This results in computed frequencies that reproduce experiment with a standard deviation of <0·31 cm-1 using nuclear masses for the motion of the three nuclei. In order to test non-Born-Oppenheimer effects different mass ratio definitions between nuclei and electrons have been analysed.

Potential energy surface of the H+3 ground state in the neighborhood of the minimum with microhartree accuracy and vibrational frequencies derived from it

The potential energy surface (PES) of the H+3 ground state is computed by means of the single and double excitation configuration interaction with an explicit linear r12 term in the wave function (CISD-R12) developed recently by the present authors, with a nearly saturated basis set. The points of the PES suggested by Meyer, Botschwina, and Burton (MBB) were chosen and the fitting procedure of the same authors was followed. The present PES has both on an absolute and a relative scale (i.e., relative to the minimum) an error of a few microhartrees (μEh) in the relevant region, an accuracy that has never before been achieved in a quantum chemical calculation for a triatomic molecule. From the fit the vibrational term values for the fundamental bands and some overtones of H+3, H2D+, HD+2, and D+3 were computed by means of the TRIATOM package of Tennyson and Miller. The computed frequencies are in better agreement with experiment (maximum error ∼0.5 cm−1) than those of all previous ab initio calculations (without empirical adjustment). To achieve this accuracy, it is necessary to go beyond the Born–Oppenheimer approximation and to take care of the finite mass ratio between nuclei and electrons.

Multiproperty determination of a new N2–Ar intermolecular interaction potential energy surface

A new multiproperty potential energy surface for the N2–Ar intermolecular interaction is reported. The present determination is based upon molecular beam total differential and integral scattering data, taken together with the temperature dependence of the interaction second virial coefficient, transport properties, transport property field effects, and relaxation phenomena, such as pressure broadening of the depolarized Rayleigh line and longitudinal nuclear spin relaxation. The primary fit has been made to the beam scattering and virial data, and refinements to the potential parameters thus determined have been made by employing the data available for the gas phase transport and relaxation phenomena. The potential energy surface employed is an empirical Morse–Morse–spline–van der Waals form, in which the potential parameters depend upon the angle between the N2 figure axis and the line joining the centers of mass of N2 and Ar. No N2 stretching dependence has been included in the present determination. Comparison is made between the present potential energy surface and two other previously published N2–Ar potential energy surfaces. The present potential energy surface provides the best overall agreement for all available gas phase data for N2–Ar mixtures, and can thus be recommended for calculations of all properties of such mixtures that depend upon the intermolecular interaction.