Theoretical and experimental studies of the isotope effects for He-CO2 and Ne-CO2 complexes

In this work, we have studied the isotope effects for the He-CO₂ and Ne-CO₂ complexes by means of theoretical calculations and experimental measurements, which were carried out using a distributed quantum cascade laser to probe a pulsed supersonic jet expansion. Firstly, infrared spectra have been recorded for the He/Ne-¹²C¹⁸O₂ complexes. Spectroscopic parameters including band origin ν₀, rotational constants A, B, C, and centrifugal distortion constants Δ_JK were obtained by fitting a Watson A-reduced Hamiltonian with 13 assigned rovibrational transitions for He-¹²C¹⁸O₂. For Ne-¹²C¹⁸O₂, the observed spectrum produces a set of spectroscopic parameters including the band origin, rotational constants and all the quartic centrifugal distortion constants with more than 100 rovibrational transitions (40 new transitions). Secondly, we have calculated the rovibrational energy levels, vibrational shifts, and rotational constants for the He/Ne-CO₂ complexes based on potential energy surfaces (PESs) and bound state calculations for ground and vibrationally excited states. The obtained results show that the spectroscopic characteristics (vibrational shifts and rotational constants) for Ne-CO₂ are analogous to those of Ar-CO₂, while those for He-CO₂ show some differences especially for the rotational constants. Finally, according to the available experimental data and our theoretical calculations, infrared spectra were predicted for six isotopologues with C_2v symmetry of Ne-CO₂ complex.

Theoretical calculation of a full-dimensional ab initio potential energy surface and prediction of infrared spectra for Xe–CS2

An effective four-dimensional (4D) ab initio potential energy surface (PES) for Xe–CS₂ which explicitly involves the intramolecular Q₁ symmetric stretching and Q₃ antisymmetric stretching vibrational coordinates of CS₂ is constructed. The computations are carried out employing single- and double-excitation coupled-cluster theory with a non-iterative perturbation treatment of triple excitations [CCSD(T)] method with a large basis set. Two vibrationally averaged potentials at the ground and ν₁ + ν₃ (ν₁ = 1, ν₃ = 1) excited states are obtained by integrating the 4D potentials over the Q₁ and Q₃ coordinates. The potentials have a T-shaped global minimum and two equivalent linear local minima. The radial discrete variable representation/angular finite basis representation and the Lanczos algorithm are employed to calculate the rovibrational energy levels for Xe–CS₂. The infrared band origin shift associated with the fundamental band of CS₂ is predicted, which is red-shifted by −1.996 cm⁻¹ in the ν₁ + ν₃ region. In addition, we further predict the spectroscopic parameters for the ground and the ν₁ + ν₃ excited states of Xe–CS₂. Compared with the previous Rg–CS₂ (Rg = He, Ne, Ar, Kr) complexes, we found that the complexes of the rare gas atoms with CS₂ display obvious regularities.

Contour plot (in cm⁻¹) of the averaged intermolecular potential energy surface for Xe–CS₂ with CS₂ at the ν₁ + ν₃ excited state.

A new ab initio potential energy surface and infrared spectra for the Ar-CS₂ complex

We report a new three-dimensional potential energy surface for Ar-CS2 involving the Q3 normal mode for the υ3 antisymmetric stretching vibration of the CS2 molecule. The potential energies were calculated using the supermolecular method at the coupled-cluster singles and doubles level with noniterative inclusion of connected triples, using augmented correlation-consistent quadruple-zeta basis set plus midpoint bond functions. Two vibrationally averaged potentials with CS2 at both the ground (υ = 0) and the first excited (υ = 1)υ3 vibrational states were generated from the integration of the three-dimensional potential over the Q3 coordinate. Each potential was found to have a T-shaped global minimum and two equivalent linear local minima. The radial discrete variable representation /angular finite basis representation method and the Lanczos algorithm were applied to calculate the rovibrational energy levels. The calculated band origin shift of the complex (0.0622 cm(-1)) is very close to the observed one (0.0671 cm(-1)). The predicted infrared spectra and spectroscopic parameters based on the two averaged potentials are in excellent agreement with the available experimental data.

NEARLY LINEAR SCALABILITY OF TIME-DEPENDENT DISCRETE VARIABLE REPRESENTATION (TDDVR) METHOD FOR THE DYNAMICS OF MULTI-SURFACE MULTI-MODE HAMILTONIAN

Time-Dependent Discrete Variable Representation (TDDVR) method was implemented by involving "classical" trajectories on each degrees of freedom (DOF) for the dynamics of multi-surface multi-mode Hamiltonian. The major focus of this article is to explore the efficiency of the serial and parallelized TDDVR algorithm for relatively large dimensional quantum dynamics in presence of non-adiabaticity among the electronic states. As a model system, the complex photoelectron spectra and non-radiative decay dynamics of trifluoroacetonitrile radical cation ( CF3CN+ ) are theoretically simulated with the aid of such parallelized algorithm, where the five lowest electronic states (X2E, A2A1, B2A2, C2A1, and D2E) of the Hamiltonian are interconnected through several conical intersections in the vicinity of Frank–Condon region with twelve (12) active vibrational modes. The Jahn–Teller splitting of the X2E and D2E states makes the coupled five-surface system to a more challenging quantum dynamical seven-surface twelve-mode model. The results obtained from the TDDVR approach show very good agreement with the profiles of both Multi Configuration Time-Dependent Hartree (MCTDH) methodology and experimental technique, where its' sequencial and parallelized algorithm depict closely linear scalability with the increasing number of basis set vis-a-vis DOFs.