The relative stabilities of the H2GeX, trans-HGeXH, and cis-HGeXH (X = O, S, Se) species and the transition states for H2GeSe ↔ trans-HGeSeH and trans-HGeSeH ↔ cis-HGeSeH isomerizations were investigated using post-Hartree−Fock ab initio methods. Geometry optimization and frequency calculations were performed at the HF, MP2, DFT, and QCISD(T) levels using TZP(2d,2p), TZP(2df,2pd), and TZP++(2df,2pd) basis sets. In the cases of oxygen and sulfur, the isomers H2GeO and H2GeS represent the structures with the highest energy, and the global minima corresponds to the trans-HGeSH and cis-HGeOH forms, respectively. In a more detailed study of the potential energy surface of the Ge[H2Se] system, we have found that the trans-HGeSeH structure is a global minimum separated at the QCISDT/TZP(2df,2pd) level by only 0.5 and 2.0 kcal/mol from H2GeSe and cis-HGSeH, respectively. In all cases the electron correlation energy plays a dominant role, and reliable assignment of the relative stability of these energetically close-lying isomers was possible using only higher levels of ab initio theory.

Hartree−Fock and post-Hartree−Fock (density functional DFT, many-body perturbation theory MP2 and MP4(SDTQ), and coupled-cluster CCSD, and CCSD[T]) quantum-mechanical methods were applied to establish molecular structures and interaction energies of the GeH2···OH2 complex. Molecular geometries of nonplanar and planar conformers were optimized at the Hartree−Fock, DFT, and MP2 levels of theory using triple-ζ-quality (TZP) augmented by sets of polarization functions (TZP(2d,2p) and TZP(2df,2pd)) basis sets. The optimized nonplanar structures correspond to minimum-energy species at all applied levels of theory. Calculated interaction energies (corrected for the basis set superposition error, CP) are relatively large and amount to −9.43 kcal/mol (MP4(CP)(SDTQ)/TZP(2df,2pd)//MP2/TZP(2df,2pd)), −9.77 kcal/mol (DFT(CP)/TZP(2df,2pd)//DFT/TZP(2df,2pd)), −8.16 kcal/mol (CCSD(CP)/TZP(2df,2pd)//MP2/TZP(2df,2pd)), and −8.90 kcal/mol at the CCSD[T](CP)/TZP(2df,2pd) levels. The optimized planar molecular structure of the studied complex (MP2/TZP(2df,2pd) level) corresponds to the transition-state form (one imaginary, 66i cm-1 harmonic vibrational frequency). A repulsive (2.07 kcal/mol) but minimum-energy planar structure of GeH2···OH2 is predicted at the DFT/TZP(2df,2pd) level of approximation. However, single-point calculations at the planar DFT-optimized geometry reveal this complex to be slightly nonbounded (0.01 kcal/mol, CCSD(CP)) or very weakly bounded (−0.17 kcal/mol, CCSD[T](CP)).

Ab initio calculations at the G2 level were used in a theoretical analysis of the kinetics of the decomposition of trifluoro-, trichloro-, and tribromomethanols. The high-pressure limiting rate coefficients k(diss,∞) for the thermal dissociation of CF(3)OH, CCl(3)OH, and CBr(3)OH were calculated using the conventional transition state theory. The results of potential surface calculations show that in the presence of the hydrogen halides HX (X = F, Cl, and Br), considerably lower energy pathways are accessible for the decomposition of CF(3)OH, CCl(3)OH, and CBr(3)OH. The mechanism of the reactions appears to be complex and consists of three consecutive elementary processes with the formation of pre- and post-reaction adducts. The presence of hydrogen halides considerably decreases the energy barrier for the bimolecular decomposition of the alcohols CF(3)OH, CCl(3)OH, and CBr(3)OH. Results of this study indicate that hydrogen halides can considerably accelerate the homogeneous decomposition of perhalogenated methanols when they are present in the reaction area at sufficiently high concentrations. However, the atmospheric concentrations of hydrogen halides are too small for efficient removal of atmospheric CF(3)OH, CCl(3)OH, and CBr(3)OH.

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