Intermolecular Potential Function for Hydroxylamine Dimer Interactions from ab initio Calculations

Abstract

Dedicated to Dr. K. Heinzinger on the occasion of his 60 th birthdayThe derivation of an intermolecular potential function for the interaction of two hydroxylamine molecules, based on ab initio SCF-ECP calculations is reported. Ab initio values were compared for selected geometries with those obtained from calculations with much larger basis sets, inluding electron correlation effects by the CEPA method. A total 658 energy values were then fitted to an analytic sum of atom-atom isotropic pair potential functions, whose functional form was given a simple electrostatic interpretation. The major difficulties, arising from the relatively low values of the stabilisation energies of the system and the numerous possibilities to form hydrogen bonds, were overcome by a careful selection of sufficient points on the potential hypersurface, introduction of cut-offs and weight factors. The obtained function was seen to be able to give a good reproduction of the interaction energies and proved suitable in a preliminary MC simulation.I n te r m o le c u la r P o te n tia l F u n c tio n fo r H y d r o x y la m in e D im e r I n te r a c tio n s fro m a b in itio C a lc u la tio n s IntroductionFor the computer simulation of liquids [1], realistic pair potentials between the molecules involved are needed.In this note we report the construction of a poten tial function for the interaction between two hydroxyl amine molecules based on ab initio SCF calculations. Hydroxylamine has been chosen for several reasons. First, being still a relatively small molecule, it allows the application of sufficient accurate ab initio calcula tions. Second, chemically situated between water and ammonia [2] and being a good solvent for electrolytes, MC and/or MD simulations of ions in hydroxylamine as solvent will be of particular interest for compari sons with similar simulations for water [3], ammonia [4] and water/ammonia mixtures [5] as solvents. Third, the possibility of forming several types of hydrogen bonds and the existence of two possible coordination sites for ions make this molecule an especially versatile and challenging example for a theoretical approach, as experimental methods for structural investigations of hydroxylamine solutions meet several restrictions that could be overcome by the quantum chemical and statistical simulation treatment.Reprint requests to Prof. Dr. B. M. Rode, Institut für Anorg. und Analytische Chemie, Universität Innsbruck, Innrain 52a. A-6020 Innsbruck. Österreich. Method Monomer Geometry and Basis SetAs a first step, full geometry optimisations by the force field method have been carried out for hydroxyl amine with various basis sets. As the results collected in Table 1 show, considerably diverging data are ob tained, and even the best of these standard basis sets do not lead to full agreement with experimental data [6]. Moreover, it could be expected from results for hydrogen peroxide and hydrazine [7], that electron correlation will be a non-negligible factor for the determination of the equilibrium geome...

The Structure of Hydroxylamine – Water Mixtures

“…For water-water interactions, the CF2 potential [3] has been used, and the potential of Michopoulos, Botschwina and Rode [8] was employed for the evalu ation of hydroxylamine-hydroxylamine pair ener gies. For water-hydroxylamine, our recently con structed potential containing the Coloumb-, r~3-, r~6-, r _9-terms and one exponential term [15], was utilized.…”

“…Further, all simulations were performed with rigid molecules. The possible errors caused by these simplifications have been inves tigated in previous studies [8,15] and were found to be well tolerable while aiming mainly at structural data.…”

“…Solvent-solvent interactions, espe cially in the case of species with hydrogen bond forma tion capacity, and the microstructures determining the properties of such mixtures are of equal interest as are the solvating properties of such mixtures for elec trolytes. Monte Carlo and molecular dynamics simu lation techniques have become a most valuable tool for such investigations, equivalent or even sometimes superior to experimental techniques.Whereas water has ben studied extensively by ex perimental and theoretical methods [1][2][3][4][5][6][7], theoretical studies still prevail for the rather unstable pure hy droxylamine [8][9][10][11][12]. With regard to the most interest ing properties of hydroxylamine -chemically situated between water and ammonia and providing 2 different hydrogen bonding sites as well as 2 potential coordi nation sites for cation binding -a systematic investi gation of mixtures of water and hydroxylamine seemed of particular interest.…”

Monte Carlo simulation of liquid hydroxylamine using ab initio intermolecular potential functions

“…In a previous note [4] details were presented of the construction of such a potential function for the intermolecular interactions of hydroxylamine (NH20H) 0 1992 John Wiley & Sons, Inc.…”

“…The main difficulties in obtaining a potential function for hydroxylamine dimer interactions originated from the fact that hydroxylamine molecules can form several types of hydrogen-bonded dimers with only minor differences in their stabilization energies. Indeed, accurate quantum mechanical calculations and careful fitting methods were required until a potential function was finally obtained [4]. In this article the potential model is reviewed (Sec.…”