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Ab initio simulation of ammonia monohydrate (NH3 center dot H2O) and ammonium hydroxide (NH4OH)
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UNSPECIFIED (2001) Ab initio simulation of ammonia monohydrate (NH3 center dot H2O) and ammonium hydroxide (NH4OH). JOURNAL OF CHEMICAL PHYSICS, 115 (15). pp. 7006-7014. ISSN 0021-9606.
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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 upper limit 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.
Item Type: | Journal Article | ||||
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Subjects: | Q Science > QC Physics | ||||
Journal or Publication Title: | JOURNAL OF CHEMICAL PHYSICS | ||||
Publisher: | AMER INST PHYSICS | ||||
ISSN: | 0021-9606 | ||||
Official Date: | 15 October 2001 | ||||
Dates: |
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Volume: | 115 | ||||
Number: | 15 | ||||
Number of Pages: | 9 | ||||
Page Range: | pp. 7006-7014 | ||||
Publication Status: | Published |
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