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The absolute vibrational energy levels of the X 2 Pi g state of O2(+) have been determined by the method of photoelectron spectroscopy in the range nu = 0-25. The precision of the method is comparable to that of conventional high resolution optical spectroscopy. The dissociation energy obtained by a linear extrapolation of the vibrational separations is found to be 6.67 plus or minus 0.18 eV.
The dissociation energy and dipole moment of the ground state of OH have been obtained with a newly developed multiconfiguration, self-consistent field plus configuration interaction CDC 7600 computer program. The computed value of the dissociation energy is 4.62 eV, which is within the uncertainty limits for the experimental value of 4.63 plus or minus 0.01 eV. The computed value of the dipole moment is 1.645 D, which is very close to the experimental result of 1.66 plus or minus 0.01 D. The present results are also compared to the data obtained from similar calculations with the BISON-MC computer program developed by Das and Wahl.
The bond dissociation energies of CH4 and C2H2 and their fragments are investigated using basis set extrapolations and high levels of correlation. The computed bond dissociation energies (D(sub e)) are accurate to within 0.2 kcal/mol. The agreement with the experimental (D(sub 0)) values is excellent if we assume that the zero-point energy of C2H is 9.18 kcal/mol. The effect of core (1s) correlation on the bond dissociation energies of C-H bonds is shown to vary from 0.2 to 0.7 kcal/mol and that for C-C bonds varies from 0.4 to 2.2 kcal/mol.
In 1986, we reported a dissociation energy (D(sub 0) of 2.31 eV for the X(sup 2)Pi ground state of MgO(+). This value was determined by computing the dissociation energy to the Mg(2+) + O(-) limit and adjusting the value to the Mg(+) + O limit using the experimental Ionization Potential (IP) of Mg(+) and the Electron Affinity (EA) of O. The success of this method relies on the assumption that there is little covalent contribution to the bonding. The very small (0.04 eV) correlation contribution to the binding energy was taken as corroboration for the validity of this approach. Our earlier theoretical value was estimated to be accurate to at least 0.2 eV. It is in excellent agreement with the subsequent value of 2.30 +/- 0.13 eV determined by Freiser and co-workers from photodissociation experiments. It is also consistent with the upper (less than 3.1 eV) and lower (greater than 1.1 eV) bounds determined by Rowe obtained by studying the reactions of Mg(+) with 03 and NO2. However, it is inconsistent with an upper bound of 1.7 eV reported by Kappes and Staley based on their failure to observe MgO(+) in the reaction of Mg(+) with N2O. The picture became somewhat clouded, however, by the recent guided-ion beam mass spectrometric studies of Dalleska and Armentrout. Their initial analysis of the reaction data for Mg(+) + O2 lead to a bond dissociation energy of 2.92 +/- 0.25 eV, which is considerably larger than the value of 2.47 +/- 0.06 eV deduced from their studies of the Mg(+)+NO2 reaction.
The dissociation energy D(0) of the X 1Sigma(+) state has been determined to be 81.5 + or - 0.5 kcal/mol. This value includes an estimate for basis set incompleteness and for core-core and core-valence correlation. The barrier in the A 1Pi state potential is estimated to be 1.9 + or - 0.2 kcal/mol. By analyzing the tunneling through the barrier, it is demonstrated that D(0) and the predissociation limit differ by about 0.8-0.9 kcal/mol. Thus the experimental predissociation limit of 82.5 + or - 0.4 kcal/mol is consistent with the values computed for D(0) and the barrier in this work.
Dissociation energies of gaseous alkali halides
The D(sub 0) values for AlH2 and AlAr are computed using the coupled cluster approach in conjunction with large basis sets. Basis set superposition and spin-orbit effects are accounted for as they are sizeable due to the small binding energy. The computed dissociation energy for AlAr is 101 /cm , which is 83% of the experimental value (122.4/ cm). Our best estimate for the H2 binding energy in AlH2 is 40 +/- 28 /cm.
Dissociation energy of gaseous titanium nitride
Dissociation energy of gaseous TiN molecule at high temperature
The bond dissociation energies (De) of C2H2, C2H4, C2H6, N2, N2H2, and N2H4 are studied at various levels of correlation treatment. The convergence of De with respect to the one-particle basis is studied at the single-reference modified coupled-pair-functional (MCPF)level. At all levels of correlation treatment, the errors in the bond dissociation energies increase with the degree of multiple bond character. The multireference configuration-interaction (MRCI) De values, corrected for an estimate of higher excitations, are in excellent agreement with those determined using the size-extensive averaged-coupled-pair-functional (ACPF) method. The full-valence complete-active-space self-consistent-field (CASSCF)/MRCI calculations are reproduced very well by MRCI calculations based on a CASSCF calculation that includes in the active space only those electrons involved in the C-C or N-N bonds.
The bond dissociation energies (D sub e) of C2H2, C2H4, C2H6, N2, N2H2, and N2H4 are studied at various levels of correlation treatment. The convergence of D sub e with respect to the one particle basis is studied at the single reference modified coupled-pair functional (MCPF) level. At all levels of correlation treatment, the errors in the bond dissociation energies increase with the degree of multiple bond character. The multireference configuration interaction (MRCI) D sub e values, corrected for an estimate of higher excitations, are in excellent agreement with those determined using the size extensive averaged coupled pair functional (ACPF) method. It was found that the full valence complete active space self consistent field (CASSCF)/MRCI calculations are reproduced very well by MRCI calculations based on a CASSCF calculation that includes in the active space only those electrons involved in the C-C or N-N bonds. To achieve chemical accuracy (1 kcal/mole) for the D sub e values of the doubly bonded species C2H4 and N2H2 requires one particle basis sets including up through h angular momentum functions (l = 5) and a multireference treatment of electron correlation: still higher levels of calculation are required to achieve chemical accuracy for the triply bonded species C2H2 and N2.
The bond dissociation energies of 1-butene and several calibration systems are computed using the G2(MP2) approach. The agreement between the calibration systems and experiment is very good. The computed values for 1-butene are compared with calibration systems and the agreement between the computed results for 1-butene and the "rule of thumb" values from the smaller systems is remarkably good.
The successive C-H bond dissociation energies of CH4, C2H2, C2H4, and H2C2O (ketene) are determined using large-basis sets and a high level of correlation treatment. For CH4, C2H2, and C2H4 the computed values are in excellent agreement with experiment. Using these results, the values 107.9 + or - 2.0 and 96.7 + or - 2.0 kcal/mol are recommended for the C-H bond dissociation energies of H2C2O and HC2O, respectively.
The requirements for very accurate ab initio quantum chemical prediction of dissociation energies are examined using a detailed investigation of the nitrogen molecule. Although agreement with experiment to within 1 kcal/mol is not achieved even with the most elaborate multireference CI (configuration interaction) wave functions and largest basis sets currently feasible, it is possible to obtain agreement to within about 2 kcal/mol, or 1 percent of the dissociation energy. At this level it is necessary to account for core-valence correlation effects and to include up to h-type functions in the basis. The effect of i-type functions, the use of different reference configuration spaces, and basis set superposition error were also investigated. After discussing these results, the remaining sources of error in our best calculations are examined.
The requirements for very accurate ab initio quantum chemical prediction of dissociation energies are examined using a detailed investigation of the nitrogen molecule. Although agreement with experiment to within 1 kcal/mol is not achieved even with the most elaborate multireference CI (configuration interaction) wave functions and largest basis sets currently feasible, it is possible to obtain agreement to within about 2 kcal/mol, or 1 percent of the dissociation energy. At this level it is necessary to account for core-valence correlation effects and to include up to h-type functions in the basis. The effect of i-type functions, the use of different reference configuration spaces, and basis set superposition error were also investigated. After discussing these results, the remaining sources of error in our best calculations are examined.
A general approach is presented for calculating the reduction of the dissociation energy of diatomic molecules immersed in a dense (n = less than 10 exp 22/cu cm) gas of molecules and atoms. The dissociation energy of a molecule in a dense gas differs from that of the molecule in vacuum because the intermolecular forces change the intramolecular dynamics of the molecule, and, consequently, the energy of the molecular bond.
Values of the bond dissociation energies, ionization potentials, and electron affinities that were taken from the literature are presented in tables for some monatomic, diatomic, and polyatomic molecules which are found in many high-temperature chemical reactions including combustion reactions. Much of the information came from literature published after 1950 which either reported experimental and theoretical energy values or gave a review of previous literature on the subject. In some cases values for the bond dissociation energies were calculated from recently published heats of formation.