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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Thermochemistry of ammonium nitrate, NH_4NO_3, in the gas phase
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Thermochemistry of ammonium nitrate, NH_4NO_3, in the gas phase

机译：气相硝酸铵NH_4NO_3的热化学

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Hildenbrand and co-workers have shown recently that the vapor above solid ammonium nitrate includes molecules of NH_4NO_3, not only NH_3 and HNO_3 as previously believed. Their measurements led to thermochemical values that imply an enthalpy change of D_(298) = 98 ± 9 kJ mol~(-1) for the gas-phase dissociation of ammonium nitrate into NH_3 and HNO_3. Using updated spectroscopic information for the partition function leads to the revised value of D _(298) = 78 ± 21 kJ mol~(-1) (accompanying paper in this journal, Hildenbrand, D. L., Lau, K. H., and Chandra, D. J. Phys. Chem. B 2010, DOI: 10.1021/jp105773q). In contrast, high-level ab initio calculations, detailed in the present report, predict a dissociation enthalpy half as large as the original result, 50 ± 3 kJ mol~(-1). These are frozen-core CCSD(T) calculations extrapolated to the limiting basis set aug-cc-pV∞Z using an anharmonic vibrational partition function and a variational treatment of the NH_3 rotor. The corresponding enthalpy of formation is Δ_fH298°(NH_4NO_3,g) = -230.6 ± 3 kJ mol~(-1). The origin of the disagreement with experiment remains unexplained.
机译：希尔登布兰德（Hildenbrand）及其同事最近表明，固体硝酸铵上方的蒸气包括NH_4NO_3分子，而不仅仅是先前认为的NH_3和HNO_3。他们的测量结果导致了热化学值，表明硝酸铵气相解离为NH_3和HNO_3的焓变为D_（298）= 98±9 kJ mol〜（-1）。将新的光谱信息用于分配函数会导致D _（298）= 78±21 kJ mol〜（-1）的修正值（本杂志随附的论文，希尔登布兰德（Hildenbrand），DL，Lau，KH和Chandra，DJ Phys Chem.B 2010，DOI：10.1021 / jp105773q）。相比之下，本报告详细介绍的高级从头算算可以预测离解焓为原始结果的一半，即50±3 kJ mol〜（-1）。这些是冻结核CCSD（T）计算，使用非谐振动分配函数和NH_3转子的变分法外推至极限基础集aug-cc-pV∞Z。相应的形成焓为Δ_fH298°（NH_4NO_3，g）= -230.6±3 kJ mol〜（-1）。与实验意见分歧的根源仍无法解释。

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