Computational study of the rovibrational spectrum of CO2-N2

Mixed quantum/classical calculations of rotationally inelastic scattering in the CO + CO system: a comparison with fully quantum results

An updated version of the CO + CO potential energy surface from [R. Dawes, X. G. Wang and T. Carrington, J. Phys. Chem. A 2013, 117, 7612] is presented, that incorporates an improved treatment of the asymptotic behavior. It is found that this new surface is only slightly different from the other popular PES available for this system in the literature [G. W. M. Vissers, P. E. S. Wormer and A. Van Der Avoird, Phys. Chem. Chem. Phys. 2003, 5, 4767]. The differences are quantified by expanding both surfaces over a set of analytic functions and comparing the behavior of expansion coefficients along the molecule-molecule distance R. It is shown that all expansion coefficients behave similarly, except in the very high energy range at small R where the PES is repulsive. That difference has no effect on low collision-energy dynamics, which is explored via inelastic scattering calculations carried out using the MQCT program which implements the mixed quantum/classical theory for molecular energy exchange processes. The validity of MQCT predictions of state-to-state transition cross sections for CO + CO is also tested by comparison against full-quantum coupled-states calculations. In all cases MQCT gives reliable results, except at very low collision energy where the full-quantum calculations predict strong oscillations of state-to-state transition cross sections due to resonances. For strong transitions with large cross sections, the results of MQCT are reliable, especially at higher collision energy. For weaker transitions, and lower collision energies, the cross sections predicted by MQCT may be up to a factor of 2-3 different from those obtained by full-quantum calculations.

A new six-dimensional ab initio potential energy surface and rovibrational spectra for the N2-CO2 complex

New six-dimensional ab initio potential energy surfaces (PESs) for the N2-CO2 complex, which involve the stretching vibration of N2 and the Q3 normal mode for the ν3 asymmetric stretching vibration of CO2, were constructed using the CCSD(T)-F12/AVTZ method with midpoint bond functions. Two vibrational averaged 4D interaction potentials were obtained by integrating over the two intramolecular coordinates. It was found that both PESs possess two equivalent T-shaped global minima as well as two in-plane and one out-of-plane saddle points. Based on these PESs, rovibrational bound states and energy levels were calculated applying the radial discrete variable representation/angular finite basis representation method and the Lanczos algorithm. The splitting of the energy levels between oN2-CO2 and pN2-CO2 for the intermolecular vibrational ground state is determined to be only 0.000 09 cm-1 due to the higher barriers. The obtained band origin shift is about +0.471 74 cm-1 in the N2-CO2 infrared spectra with CO2 at the ν3 zone, which coincides with the experimental data of +0.483 74 cm-1. The frequencies of the in-plane geared-bending for N2-CO2 at the ν3 = 0 and 1 states of CO2 turn out to be 21.6152 and 21.4522 cm-1, the latter reproduces the available experimental 21.3793 cm-1 value with CO2 at the ν3 zone. The spectral parameters fitted from the rovibrational energy levels show that this dimer is a near prolate asymmetric rotor. The computed microwave transitions as well as the infrared fundamental and combination bands for the complex agree well with the observed data.

Weakly-bound clusters of atmospheric molecules: infrared spectra and structural calculations of (CO2)n-(CO)m-(N2)p, (n,m,p) = (2,1,0), (2,0,1), (1,2,0), (1,0,2), (1,1,1), (1,3,0), (1,0,3), (1,2,1), (1,1,2)

Structural calculations and high-resolution infrared spectra are reported for trimers and tetramers containing CO₂ together with CO and/or N₂. Among the 9 clusters studied here, only (CO₂)₂-CO was previously observed by high-resolution spectroscopy. The spectra, which occur in the region of the ν₃ fundamental of CO₂ (≈2350 cm^-1), were recorded using a tunable optical parametric oscillator source to probe a pulsed supersonic slit jet expansion. The trimers (CO₂)₂-CO and (CO₂)₂-N₂ have structures in which the CO or N₂ is aligned along the symmetry axis of a staggered side-by-side CO₂ dimer unit. The observation of two fundamental bands for (CO₂)₂-CO and (CO₂)₂-N₂ shows that this CO₂ dimer unit is non-planar, unlike (CO₂)₂ itself. For the trimers CO₂-(CO)₂ and CO₂-(N₂)₂, the CO or N₂ monomers occupy equivalent positions in the 'equatorial plane' of the CO₂, pointing toward its C atom. To form the tetramers CO₂-(CO)₃ and CO₂-(N₂)₃, a third CO or N₂ monomer is then added off to the 'side' of the first two. In the mixed tetramers CO₂-(CO)₂-N₂ and CO₂-CO-(N₂)₂, this 'side' position is taken by N₂ and not CO. In addition to the fundamental bands, combination bands are also observed for (CO₂)₂-CO, CO₂-(CO)₂, and CO₂-(N₂)₂, yielding some information about their low-frequency intermolecular vibrations.

Fully quantum calculations of O2-N2 scattering using a new potential energy surface: Collisional perturbations of the oxygen 118 GHz fine structure line

A proper description of the collisional perturbation of the shapes of molecular resonances is important for remote spectroscopic studies of the terrestrial atmosphere. Of particular relevance are the collisions between the O₂ and N₂ molecules-the two most abundant atmospheric species. In this work, we report a new highly accurate O₂(X³Σ_g ^-)-N₂(X¹Σ_g ⁺) potential energy surface and use it for performing the first quantum scattering calculations addressing line shapes for this system. We use it to model the shape of the 118 GHz fine structure line in O₂ perturbed by collisions with N₂ molecules, a benchmark system for testing our methodology in the case of an active molecule in a spin triplet state. The calculated collisional broadening of the line agrees well with the available experimental data over a wide temperature range relevant for the terrestrial atmosphere. This work constitutes a step toward populating the spectroscopic databases with ab initio line shape parameters for atmospherically relevant systems.

Correction: Quantum tunneling dynamical behaviour on weakly bound complexes: the case of a CO2-N2 dimer

Correction for 'Quantum tunneling dynamical behaviour on weakly bound complexes: the case of a CO2-N2 dimer' by Miguel Lara-Moreno et al., Phys. Chem. Chem. Phys., 2019, 21, 3550-3557, DOI: 10.1039/c8cp04465a.