The structure of the O2–N2O complex

Abstract

We have investigated the lowest energy structures and interaction energies of the oxygen nitrous oxide complex (O2-N2O) using explicitly correlated coupled cluster theory. We find that the intermolecular potential energy surface of O2-N2O is very flat, with two minima of comparable energy separated by a low energy first order saddle point. Our results are able to conclusively distinguish between the two sets of experimental geometric parameters for O2-N2O that were previously determined from rotationally resolved infrared spectra. The global minimum structure of O2-N2O is therefore found to be planar with a distorted slipped parallel structure. Finally, we show that the very flat potential energy surface of O2-N2O is problematic when evaluating vibrational frequencies with a numerical Hessian and that consideration should be given as to whether results might change if the step-size is varied.

Structure and Abundance of Nitrous Oxide Complexes in Earth’s Atmosphere

“…Song et al also recorded rotationally resolved infrared spectra of O 2 –N 2 but only determined the intermolecular distance and not the intermolecular angles . Very recently, we showed that the distorted slipped parallel structure of O 2 –N 2 O shown in Figure is the global minimum and is ∼0.3 kJ mol –1 lower in energy than the alternative local minimum slipped parallel structure (where the O 2 subunit is distal to the O of N 2 O) . The structure of the Ar–N 2 O complex has been extensively studied by rotational resonance and rotationally resolved vibrational spectroscopy. − The nearly T-shaped experimental structure, whereby Ar is slightly tilted toward the O of N 2 O, is in excellent agreement with our calculated CCSD­(T)-F12b/CBS structure.…”

“…The calculated vibrational ground state values are obtained by adding vibrational–rotational coupling terms calculated using VPT2 at the CCSD­(T)/aug-cc-pV­(T+d)­Z level of theory to the equilibrium CCSD­(T)-F12b aug-cc-pV­(T+d)­Z/aug-cc-pV­(Q+d)­Z CBS results. Note that we were unable to obtain sensible vibrational–rotational coupling terms for O 2 –N 2 O due to the extremely flat potential energy surface around its equilibrium structure . Despite attempts to further tighten the convergence criteria or change the numeric step-size, we were unable to obtain stable cubic force constants for O 2 –N 2 O.…”

“…The optimization threshold criteria were set to gradient = 1 × 10 –6 au, stepsize = 1 × 10 –6 au, and energy = 1 × 10 –8 au, with all single point energies converged to 1 × 10 –9 au. However, for the N 2 O–O 2 complex, even tighter convergence criteria were found to be necessary to accurately describe the very flat potential energy surface near the global minimum . In this case the optimization thresholds were as follows: gradient = 1 × 10 –8 au, stepsize = 1 × 10 –8 au, and energy = 1 × 10 –10 au, with all single point energies converged to energy = 1 × 10 –10 au, orbital = 1 × 10 –9 au, coeff = 1 × 10 –9 au and the Hartree–Fock density matrix converged to accu = 1 × 10 –20 au.…”

Ab initio studies on complexes of ozone with triatomic and larger molecules.

“…No literature could be found on the O 3 -N 2 O complex. The N 2 O complex with O 2 was discussed by Salmon and Lane [29]. Its structure was found to be planar slipped parallel, having a CCSD(T)-F12b/AVQZ dissociation energy of 280 cm − 1 .…”

Theoretical study of the CO2–O2 van der Waals complex: potential energy surface and applications

“…To date, there are numerous theoretical and experimental studies dedicated to vdW complexes involving CO 2 as well as O 2 with other molecules such as CO 2 –O 2 , 10–12 O 2 –O 2 , 11,13 O 2 –N 2 , 14 O 2 –N 2 O, 4,15 CO 2 –H 2 , 16 CO 2 –CO 2 , 5,17 CO 2 –N 2 , 18,19 CO 2 –CO, 6,18,20 and CO 2 –N 2 O. 21 To the best of our knowledge, no analytical function of the CO 2 –O 2 PES is available in the literature.…”