Ab Initio-Based Global Double Many-Body Expansion Potential Energy Surface for the First²A″ Electronic State of NO₂

Abstract

An ab initio-based global double many-body expansion potential energy surface is reported for the first electronic state of the NO(2)((2)A") manifold. Up to 1700 ab initio energies have been employed to map the full configuration space of the title molecule, including stationary points and asymptotic channels. The calculated grid energies have been scaled to account for the incompleteness of the basis set and truncation of the MRCI expansion and fitted analytically with a total root-mean-squared-deviation smaller than 1.0 kcal mol(-1). The lowest point of the potential energy surface corresponds to the (2)B(1) linear minimum, which is separated from the C(s) distorted minimum by a C(2v) barrier of ≈9.7 kcal mol(-1). As usual, the proposed form includes a realistic representation of long-range interactions. Preliminary work indicates its reliability for reaction dynamics.

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

“…More recently, a double many body expansion fit to 1700 points at the MRCI/aug-cc-VQZ level of theory for the 2 A 00 state was carried out. 17 In addition, quasi classical trajectory (QCT) calculations 2,9,13,18 have been reported for the temperature dependent rate for the N( 4 S) + O 2 -NO + O and its reverse reaction using different PESs.…”

“…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)…”

Modeling Cusps in Adiabatic Potential Energy Surfaces

“…The first step consists of defining the parametric equation that locates the crossing seam. Because it occurs at geometries with C 2v symmetry, 23,24 …”

“…For convenience, we focus here on the lowest adiabatic sheet for which accurate ab initio calculations are affordable and compare the results with previously reported fits. 24 The new global PES reported so obtained is compared with two distinct DMBE forms. 24 They are all based on …”

“…24 The new global PES reported so obtained is compared with two distinct DMBE forms. 24 They are all based on …”