Abstract:

Enthalpy changes of the reactions involved in our previous papers have been re-examined at the G2(MP2) and G2 levels. The G2(MP2) and G2 energies of Ar, Ar+,ArAr+, ArCl+, ArF+, ArH+, ArHe+, ArNe+, ArO+, ArS+, H2+, He, HeCl+, HeF+, HeO+,HeS+, Ne, NeCl+, NeF+, NeO+ and NeS+ have been calculated. The G2(MP2) and G2 results for all of the interested reactions have also been compared with those of the previous MP2/6-31G** and MP4/6-311G (2df, 2pd) calculations. All of the G2(MP2) and G2 reaction enthalpies are improved from the MP2 and MP4 level of calculations when compared with the experimental data for the four categories of reactions as (1) iso-electronic, iso-gyric; (2) valence isoelectronic, isogyric; (3) and (4)non-isogyric reactions with the average absolute deviations of 5.10, 4.60, 7.70 and 9.20 for G2(MP2) and 4.18, 5.19, 6.78 and 6.49kJ•mol-1 for G2, respectively. The individual deviation for almost all of the reactions involved in this work is not more than ±13 kJ•mol-1 for G2(MP2) and ±8.4 kJ•mol-1 for G2. In this paper, an additional number of reactions examined at the G2(MP2) and G2 levels as well as at the MP2/6-31G** and MP4/6-311G(2df, 2pd) levels of calculations have also been reported. The MP2, MP4, G2(MP2) and G2 total energies for the interested chemical species have been calculated if these energies have not been reported in literatures. All of the reaction energies at different levels have been compared with the experimental data in a number of reactions devided into the above four categories. The average absolute deviations are 25.9, 36.0, 29.2 and 40.1 for MP2; 8.41, 18.3, 17.2 and 18.3 for MP4; 9.41, 5.98, 4.85 and 6.90 for G2(MP2) and 6.69, 4.06, 3.85 and 4.60 kJ•mol-1 for G2, respectively. It is clear that the MP2 calculation did quite poor for all of the four categories of reactions and the MP4 did well only for the isoelectronic and isogyric reactions. The G2(MP2) and G2 reproduce the experimental reaction enthalpy changes very well for all reactions in the four categories. The individual deviation for almost all of the reactions involved in this work is not more than ±13 kJ•mol-1 for G2(MP2) and ±8.4 kJ•mol-1 for G2 while it may be more than ±84 kJ•mol-1 for MP2/6-31G**.

Key words: MP4, G2 theory, G2(MP2), Isoelectronic, Isogyric, Non-isogyric, Enthalpy