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Titolo:
Ab initio simulation of ammonia monohydrate (NH3 center dot H2O) and ammonium hydroxide (NH4OH)
Autore:
Fortes, AD; Brodholt, JP; Wood, IG; Vocadlo, L; Jenkins, HDB;
Indirizzi:
Birkbeck Coll, Res Sch Geol & Geophys Sci, London WC1E 6BT, England Birkbeck Coll London England WC1E 6BT phys Sci, London WC1E 6BT, England Univ Coll London, London WC1E 6BT, England Univ Coll London London England WC1E 6BT ondon, London WC1E 6BT, England Univ Warwick, Dept Chem, Coventry CV4 7AL, W Midlands, England Univ Warwick Coventry W Midlands England CV4 7AL 7AL, W Midlands, England
Titolo Testata:
JOURNAL OF CHEMICAL PHYSICS
fascicolo: 15, volume: 115, anno: 2001,
pagine: 7006 - 7014
SICI:
0021-9606(20011015)115:15<7006:AISOAM>2.0.ZU;2-#
Fonte:
ISI
Lingua:
ENG
Soggetto:
HYDROGEN-BONDS; ICY SATELLITES; WATER; EQUATION; STATE; ION; DIFFRACTION; TRANSITION; CRYSTALS; VIII;
Tipo documento:
Article
Natura:
Periodico
Settore Disciplinare:
Physical, Chemical & Earth Sciences
Citazioni:
48
Recensione:
Indirizzi per estratti:
Indirizzo: Fortes, AD Birkbeck Coll, Res Sch Geol & Geophys Sci, Gower St, London WC1E 6BT, England Birkbeck Coll Gower St London England WC1E 6BT 1E 6BT, England
Citazione:
A.D. Fortes et al., "Ab initio simulation of ammonia monohydrate (NH3 center dot H2O) and ammonium hydroxide (NH4OH)", J CHEM PHYS, 115(15), 2001, pp. 7006-7014

Abstract

We report the results of the first pseudopotential plane-wave simulations of the static properties of ammonia monohydrate phase I (AMH I) and ammonium hydroxide. Our calculated fourth-order logarithmic equation of state, at zero pressure and temperature, has molar volume, V-0=36.38(3) cm(3) mol(-1), bulk modulus, K-0=9.59(9) GPa, and the first derivative of the bulk modulus with respect to pressure, K-0(')=5.73(21). Both this and the lattice parameters are in very good agreement with experimental values. The monohydrate transforms, via a solid-state proton transfer reaction, to ammonium hydroxide (NH4OH) at 5.0(4) GPa. The equation of state of ammonium hydroxide is,V-0=31.82(5) cm(3) mol(-1), K-0=14.78(62) GPa, K-0(')=2.69(48). We calculate the reaction enthalpy, DeltaH(NH4OH,s --> NH3.H2O,s)=-14.8(5) kJ mol(-1)at absolute zero, and thus estimate the enthalpy of formation, Delta H-f(circle minus)(NH4OH,s)=-356 kJ mol(-1) at 298 K. This result places an upperlimit of 84 kJ mol(-1) on the barrier to rotation of the ammonium cation, and yields an average hydrogen bond enthalpy of similar to 23 kJ mol(-1). (C) 2001 American Institute of Physics.

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Documento generato il 30/11/20 alle ore 09:58:59