Modelling the structure of the water molecule under both local environmental constraints and explosive conditions
Faculty of Sciences. Physics
Physics and chemistry of liquids. - London
, p. 471-473
University of Antwerp
A model proposed by Gabbay and March allowed the geometry of the water molecule to be studied as the OH bond length was compressed from its equilibrium value; the corresponding H-O-H bond angle opened up from 104° and under extreme compression a limiting angle of 180° was predicted. Local environmental changes were later found to increase the bond angle of 104° by some degrees. Such structural changes are compared here and contrasted with molecular dynamics results of Schwegler et al. (Schwegler, Galli and Gygi, Phys. Rev. Lett. 84, 2429 (2000)) on water under pressure, and with subsequent simulations by Wu et al. (Wu, Fried, Yang, Goldman and Bastea, Nat. Chem. 1, 57 (2009)) involving the high-explosive pentaerythritol tetranitrate. Extreme conditions of both pressure and temperature lead to a homolytic dissociation reaction involving free atoms and radicals: H2O ⇌ H + OH, in marked contrast to ambient conditions that favour the heterolytic self-ionisation. The X-ray induced homolytic dissociation of water and formation of an O2 + H2 crystalline alloy at high pressure as observed by Mao et al. (Mao, Mago, Meng, Eng, Hu, Chow, Cai, Shu and Hemley, Science 314, 636 (2006)) are also noted.