The Structure of Hydroxylamine – Water Mixtures

Abstract

T h e S t r u c t u r e o f H y d r o x y la m in e -W a te r M ix tu r e s Results of M onte Carlo Simulations Sergi Vizoso and Bernd M. Rode Institute for General, Inorganic and Theoretical Chemistry, University of Innsbruck, Innrain 52 a, A-6020 Innsbruck, Austria Z. Naturforsch. 50a, 263-273 (1995); received September 24, 1994 Dedicated to Prof. H. Ohtaki on the Occasion of his 60th Birthday Monte Carlo simulations have been carried our for 5, 25, 50, and 75 weight% aqueous solutions of hydroxylamine. Changes in the microstructure of the solutions have been evaluated by means of radial and angular distribution functions, coordination number distributions and pair energy anal ysis. The structure of liquid hydroxylamine is strongly altered by even small amounts of water, whereas water clusters similar to the pure water are maintained up to higher NH2OH concentra tions. The structural entities in the mixtures are determined by hydrogen bonding and electrostatic arrangement of ligands. IntroductionSolvent mixtues are of great interest not only be cause of their practical applications in mediating and influencing chemical processes, but also from a theo retical viewpoint. 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. So far, theoretical studies have been reported for hydrogen bonded pairs of both spe cies in the gas phase [13,14], and recently a potential function for the H 20 /N H 20 H energy surface has been presented [15], which also forms the basis for our Reprint requests to Prof. B. M. Rode.further investigations of the condensed system by means of simulation techniques.In order to obtain information about the microstructure of hydroxylamine/water mixtures, Monte Carlo simulations have been carried out for mixtures with the mole fraction of NH2OH varying from 0.025 to 0.625. The results have been analyzed in terms of radial and angular distribution functions (RDF, ADF), coordination number distributions and H-bonding features. Method Intermolecular PotentialsFor water-water interactions, the CF2 potential [3] has been used, and the potential of Michopoulos, Botschwina and Rode [8] was employed for ...

Liquid Structure and Hydrogen Bonding in Aqueous Hydroxylammonium Nitrate

“…Although the RDFs for hydroxylammonium oxygen (O h , Figure S3) do show weak interactions, represented by shoulders around 3 Å, these are not included in our subsequent analysis due to their weak nature. This observation aligns with previous simulations of its conjugate base NH 2 OH . The locations of the first maximum and minimum for each RDF, which indicate the primary peak positions and the start of the second coordination shell, respectively, are summarized in Table .…”

“…This observation aligns with previous simulations of its conjugate base NH 2 OH. 48 The locations of the first maximum and minimum for each RDF, which indicate the primary peak positions and the start of the second coordination shell, respectively, are summarized in Table 2. These positions suggest moderately strong hydrogen bonds, with the bond strength increasing as the distance to the first maximum decreases.…”

Effect of NH2OH on Etching Characteristics of Si{100} in KOH Solution

“…It may be because of the decrease in NH 2 O − and OH − ions concentration and/or decrease in freely available water due to the formation of clusters (K + , OH − , NH 2 O − , etc). 40,41 Apart from an increased etch rate of Si{100} surface, a good etchant should also exhibit good etch selectivity between the substrate (e.g. silicon) and masking material (e.g.…”

Etching characteristics of Si{110} in 20 wt% KOH with addition of hydroxylamine for the fabrication of bulk micromachined MEMS

“…The major objective of this work is to investigate the effect of NH 2 OH to achieve high etch rate and undercutting to promote the application of wet anisotropic etching in MEMS fabrication. In several studies, it has been claimed that the etch rate of an etchant increases if its wettability improves such as the wettability of KOH increases when anionic additives are added [35,36] [40,41].…”