Double-valued potential energy surface for H2O derived from accurate ab initio data and including long-range interactions

Abstract

In a recent work we have been able to model the long-range interactions within the H 2 O molecule. Using these long-range energy terms, a complete potential energy surface has been obtained by fitting high-quality ab initio energies to a double-valued functional form in order to describe the crossing between the two lowest-potential-energy surfaces. The two diabatic surfaces are represented using the double many-body expansion model, and the crossing term is represented using a three-body energy function. To warrant a coherent and accurate description for all the dissociation channels we have refitted the potential energy functions for the H 2 ( 3 ⌺ u ϩ ), OH( 2 ⌸), and OH( 2 ⌺) diatomics. To represent the three-body extended Hartree-Fock nonelectrostatic energy terms, V 1 , V 2 , and V 12 , we have chosen a polynomial on the symmetric coordinates times a range factor in a total of 148 coefficients. Although we have not used spectroscopic data in the fitting procedure, vibrational calculations, performed in this new surface using the DVR3D program suite, show a reasonable agreement with experimental data. We have also done a preliminary quasiclassical trajectory study ͑300 K͒. Our rate constant for the reaction O(, is very close to the most recent recommended value. This kinetic result reinforces the importance of the inclusion of the long-range forces when building potential energy surfaces.

Dynamical studies and product analysis of O(1D) + H2/D2reactions

“…OH þ H and its isotopic variants have been the subject of various experimental studies [1][2][3][4][5][6][7][8]. Numerous theoretical studies of its dynamics have also been carried out (for example, see [1,[5][6][7][9][10][11][12][13][14][15][16][17][18][19][20]) using the potential energy surfaces (PES) published for this system [9,[21][22][23][24][25][26][27][28][29][30][31][32].…”

Using the Reactions O+H₂ → OH+H to Explore the Importance of the Atomic Quantum States on Chemical Kinetics and Reaction Dynamics

“…We have studied theoretically theses reactions in the past 13,19,[23][24][25] , and here, using some of our previous trajectories calculations results, we can show that two different types of dynamical behaviour can be exemplified by these two reactions.…”

“…In addition, this Σ PES correlates with the product OH diatomic in its first excited state, OH( 2 Σ) and does not contribute to the title reaction at the energies of chemical practical interest. To illustrate the main differences between these reactions, here we use two of our published a PESs 23,24 for singlet and triplet state of this system as examples. The Figure 3 is a three dimensional view of an O( …”

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“…Recently, mainly based on the very accurate ab initio results of Partridge and Schwenke [66] complemented with other data [68,69] and on a careful description of the long range interactions between the different dissociation channels [70], Brandão and Rio presented another double-valued PES for this system [43]. This BR PES displays a small van der Waals minimum and a small saddle point under the dissociation limit for the C 2v approach of the O ( 1 D) atom to the H 2 molecule and a very small barrier (< 0.4 kJ mol −1 ) to collinear addition ( 1 Σ + surface) in agreement with the findings of Walch and Harding [68].…”

“…Numerous theoretical studies of its dynamics have also been carried out, for example see [11,13,[16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31], using several potential energy surfaces (PESs) published for this system [29,[32][33][34][35][36][37][38][39][40][41][42][43]. These works have been the subject of partial reviews by Liu [44], Althorpe and Clary [45], Balucani et al [46] and Aoiz et al [47].…”