The electronic structure of the ground and low-lying states of the diatomic fluorides TiF, VF, CrF, and MnF was examined by multireference and coupled cluster methods in conjunction with extended basis sets. For a total of 34 states we report binding energies, spectroscopic constants, dipole moments, separation energies, and charge distributions. In addition, for all states we have constructed full potential curves. The suggested ground state binding energies of TiF(X (4)Phi), VF(X (5)Pi), CrF(X (6)Sigma(+)), and MnF(X (7)Sigma(+)) are 135, 130, 110, and 108 kcal/mol, respectively, with first excited states A (4)Sigma(-), A (5)Delta, A (6)Pi, and a (5)Sigma(+) about 2, 3, 23, and 19 kcal/mol higher. In essence all our numerical findings are in harmony with experimental results. For all molecules and states studied it is clear that the in situ metal atom (M) shows highly ionic character, therefore the binding is described realistically by M(+)F(-).

Employing multireference configuration interaction and coupled-cluster methods in conjunction with quantitative basis sets, we have explored the electronic structure of the charged diatomic fluorides MF(+/-), where M=Sc, Ti, V, Cr, and Mn. In addition, and in order to complete our recently published work on the neutral diatomic fluorides MF, M=Ti-Mn, we have also examined the ground (X (1)Sigma(+)) and the first excited state (alpha (3)Delta) of neutral ScF. For the entire anionic MF(-) series and the cations ScF(+), VF(+), and MnF(+), no experimental or theoretical results of any kind have been reported so far in the literature. For the charged MF(+/-) sequence we have investigated a total of 43=29(MF(+))+14(MF(-)) states, reporting potential energy curves, energetics, and common spectroscopic parameters. Two are the most interesting conclusions of the present work. (a) The Coulombic binding character of MF(+) cations, i.e., the conformity of their equilibrium description to M(2+)F(-) and (b) the atypical bonding of the MF(-) anions and their surprisingly high dissociation energies (up to 85 kcal/mol for the X (2)Delta state of ScF(-)). Considering the complexities of these chemically "simple" systems, our results on ScF, TiF(+), and CrF(+) are in very good agreement with the limited experimental findings.

The electronic and geometric structure of the 3d-transition metal monocarbonyls MCO, M=Sc, Ti, V, and Cr was investigated through coupled cluster (CC) and multireference variational methods (MRCI) combined with large basis sets. For the ground and a few low-lying excited states complete potential energy profiles were constructed at the CC-level of theory. The M-CO dissociation energies of the ground states X 4Sigma-,X 5Delta,X 6Sigma+, and X 7A' are calculated to be 36, 27, 18, and 2 kcal/mol for ScCO, TiCO, VCO, and CrCO, with respect to Sc(4F),Ti(5F),V(6D),Cr(7S)+CO(X 1Sigma+). The bonding is rather complicated and could be attributed mainly to pi-conjugation effects between the M and CO pi-electrons, along with weak sigma-charge transfer from CO to M atoms. Almost in all cases the metal atoms appear to be slightly positively charged, at least according to the direction of the dipole moment vectors and the MRCI population densities.

The titled molecular species have been studied by ab initio multireference and coupled-cluster methods in conjunction with large correlation consistent basis sets. A total of 71 MCl, 13 MCl(+), and 9 MCl(-) states, M = Sc, Ti, V, Cr, have been examined. We report total energies, dissocation energies, spectroscopic parameters, and full potential energy curves. Most of our results are presented for the first time in the literature, whereas the general agreement with available experimental data can be considered as quite good.

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