ACCURATE ENTHALPIES OF FORMATION FOR CRX(G), X = O, OH, AND F - A COMPUTATIONAL STUDY

CrOH(g) is studied for the first time by theory, using accurate config uration interaction (CI) methods in conjunction with large basis sets. The ground and lowest excited state are established for the neutral a nd singly ionized molecule. The ionization potential is computed to 7. 54 +/- 0.05 eV, which, when applied to experimental results for CrOH[Magnera, T. F.; David, D. E.; Michl, J. J. Ain. Chem. Sec. 1989, 111, 4100. Kang, H.; Beauchamp, J. L. J. Am. Chem. Sec. 1986, 108, 7502] o pens access to experimental data on the bond dissociation energy in Cr -OH. Accurate quantum chemical methods have been applied to the calcul ation of bond dissociation energies of gaseous CrOH, CrF, and CrO. For the singly bound molecules the values obtained, D-0(Cr-OH) = 3.74 +/- 0.10 eV and D-0(CrF) = 5.04 +/- 0.10 eV, constitute the most accurate thermodynamical data available for these compounds. The high accuracy has been realized through the use of a dissociation process which is analogous to electron-attachment induced dissociation, leading to a hi gh degree of cancelation of errors in the calculation of bond strength s in polar systems. In chromium monoxide, higher-than-triply excited c onfigurations are important in the CI expansion, and an extrapolation procedure is applied to take these effects into account. The resulting estimate, D-0(CrO) = 4.69 +/- 0.10 eV, confirms the experimental find ing of Kang and Beauchamp [Kang, H.; Beauchamp, J. L. J. Am. Chern. So c. 1986, 108, 5663]. Enthalpies of formation are calculated for the ti tle molecules based on the computed bond dissociation energies.