A realistic multi-sheeted potential energy surface for NO2(2A′) from the double many-body expansion method and a novel multiple energy-switching scheme

Abstract

We report a new multi-sheeted double many-body expansion potential energy surface that reproduces most known topological features of the title system. Near spectroscopic accuracy is conveyed to the ground-state sheet of 2A1 (1 2A′ in Cs) symmetry in the vicinity of the minimum by merging it with a spectroscopically determined Taylor-series-expansion-type form via a novel multiple energy-switching scheme. A high energy ridge for C2v insertion of N(4S) into O2(X 3Σg−) has also been imposed to mimic the result of accurate ab initio complete active space self-consistent field and second-order perturbation theory on CAS wave function calculations carried out for such geometries. This ridge decreases for Cs geometries yielding a minimum barrier height for the N+O2 reaction of 0.273 eV at a bent N–O–O structure defined by RNO=3.107a0, ROO=2.513a0, and ∠NOO=113.5 deg. Both the location and height of this barrier are in good agreement with existing ab initio calculations and the recommended values. Another salient feature is a shallow minimum on the à 2B2 potential energy surface that is separated from the absolute X̃ 2A1 minimum by a conical intersection. Such a feature is accurately predicted by the newly reported ab initio calculations and well mimicked by the global double many-body expansion/energy-switching potential energy surface here reported. This is therefore commended both for spectroscopic and reactive dynamics studies on the title system. A final comment in relation to the conical intersection and the energy-switching scheme goes to the expected accuracy of current approaches for spectroscopically determined effective single-valued forms.

The N(4S) + O2(X3Σ−g) ↔ O(3P) + NO(X2Π) reaction: thermal and vibrational relaxation rates for the 2A′, 4A′ and 2A′′ states

“…14 This was followed by a PESs for the 2 A 0 state using a diatomics in molecules (DIM) expansion with the two-body terms based on extended Hartree-Fock calculations. 15 Then, a 2-dimensional PES with the NO bond length fixed at its equilibrium value of 2.176 a 0 was determined at the icMR-CI+Q/cc-pVQZ level of theory and represented as a cubic spline. 16 This work also presented a PES for the 2 A 00 state.…”

“…This experiment found a rate of k n=1-0 = 4.2 AE 0.7(10 À11 ) cm 3 s À1 at T = 295 K which is larger by 75% compared with the earlier experiments. 3 Quite recent QCT simulations using again the DIM-based PES 15 mentioned above reported a rate of k n=1-0 = 4.34 AE 0.7(10 À11 ) cm 3 s À1 at T = 298 K from QCT simulations 21 which used the empirical DIM PES for the 2 A 0 ground state 15 and a more recent, MRCI-based fitted PES for the 2 A 00 state. 17 Given the rather heterogeneous situation for the quality of the existing PESs for studying the N( 4 S) + O 2 (X 3 S À g ) reaction and the vibrational relaxation of NO, the present work determines fully dimensional PESs using a consistent methodology to represent the 3 lowest electronic states, 2,4 A 0 and 2 A 00 as well as to evaluate the cross sections for the (forward)…”

Reactive molecular dynamics: From small molecules to proteins

“…91 The Sorbie-Murrell potential is based on a DIM expansion combined with a many body expansion. 148,153 Further along these lines, a DIM-based double many body expansion (DMBE) PES has been developed 154 and used in QCT simulations. 144 Using this DMBE PES the rate k + (T) for the forward reaction (N + O 2 !…”

C n ( n =2−4): current status

“…To improve the C 3 DMBE II PES at the linear global minima, we used [117] a simplified version of Varandas' ES scheme [173] to morph DMBE II and the ABW [34] and SS [115] local functions. Both DMBE/ES/ABW and DMBE/ES/SS PESs so obtained [117] read [84,172].…”

“…where x = ABW or SS, and f ( E) is defined by [173] f In turn, E = E − E min is the energy displacement with respect to the absolute global minima of the DMBE II PES, and E 0 = E 0 − E min is the energy difference between E min and the cut-off energy E 0 . Finally, β is a trial-and-error parameter, n is an even integer and ξ a small number chosen to avoid numerical overflows at E = E min .…”