Marzio Rosi

The binding energies of one and two water molecules to the first transition‐row metal positive ions

The bonding of water to the transition metal positive ions is electrostatic in origin. The electrostatic bonding is enhanced by a variety of mechanisms: mixing in 4p character, 4s–3d hybridization, and 4s promotion into the compact 3d orbital. The importance of these effects varies between the different metal ions due to changes in the separation of the metal ion atomic states. Furthermore the changes in the metal–water repulsion when a second water is added also changes the relative importance of the different metal asymptotes. The second water binding energy varies from being 11 kcal/mol smaller than the first for Mn+ to 3 kcal/mol larger for V+ and Fe+.

Theoretical studies of the first- and second-row transition-metal mono- and dicarbonyl positive ions

Ab initio calculations have been carried out on the first‐ and second‐row transition‐metal mono‐ and dicarbonyl positive ions. The bonding in these systems is discussed in detail. Trends in the series of mono‐ and dicarbonyl ions and between the first‐ and second‐row transition metals are explained in terms of a dominantly electrostatic bonding interaction and differences in metal ion state separations, ionization potentials, and s and d orbital sizes. Dissociation energies are presented and a detailed comparison is made with experimental data. Where reliable experimental data exists, agreement with the theoretical results is generally good. An exception is Mo(CO)+1,2, where the computed binding energies are much smaller than the experimental values.

An ab initio study of Fe(CO)n, n = 1,5, and Cr(CO)6

Ab initio calculations have been performed for Cr(CO)6 and Fe(CO)n, n=1,5. Basis sets of better than double zeta quality are used and correlation is included using the modified coupled‐pair functional method. The computed geometries and force constants are in reasonable agreement with experiment. The sequential bond dissociation energies of CO from Fe(CO)5 are estimated to be: 39, 31, 25, 22, and ≳5 kcal/mol. We note that the first bond dissociation energy is relative to the singlet ground state of Fe(CO)5 and the lowest singlet state of Fe(CO)4, whereas the second is relative to the ground triplet states of Fe(CO)4 and Fe(CO)3. In addition, the binding energy for Fe–CO would be modified to 18 kcal/mol if dissociation occurred to the Fe(5F) excited state asymptote. The CO binding energies for Fe and Cr are found to be in poorer agreement with experiment than those found in a previous study on Ni(CO)4. The origins of this difference are discussed.

On the binding energy of Hen+, for n = 2–7

The atomization energy of small positively charged He clusters has been studied using ab initio methods that include correlation. The atomization energy increases monotonically with cluster size. The inclusion of correlation changes the nature of the bonding and hence changes the structure of the most stable cluster.

A theoretical study of the low-lying states of Ti2 and Zr2

The 1Σ+g, 3Δg, 3Σ+u, and 7Σ+u states of Ti2 and Zr2 have been studied using a multireference configuration‐interaction (MRCI) approach. Although our best calculation produces a 1Σ+g ground state for Zr2, the 3Σ+u and 3Δg states are found to be very low lying. Additional support for a 1Σ+g ground state assignment comes from the fact that the resulting vertical excitation spectrum is consistent with the optical spectrum of Zr2 observed in noble gas matrices. For Ti2, it proved more difficult to make a definitive assignment of the ground state, because of the many low‐lying states and the large effect of inner‐shell (3s and 3p) correlation. With only valence correlation included, the ground state is predicted to be 7Σ+u at both the MRCI and averaged coupled‐pair functional (ACPF) levels of correlation treatment. However, inner‐shell correlation effects, estimated based on modified coupled‐pair functional (MCPF) and contracted configuration‐interaction (CCI) calculations, preferentially lower the 1Σ+g and 3Δg...

On the bonding in Be22

Abstract The ground 1 Σ g + state and excited 3 Π u and 1 Π u states of Be 2 2+ have been studied. The ground state has 13 vibrational levels with an appreciable lifetime with respect to unimolecular decay. The 3 Π u state also has an inner well with several vibrational levels with long lifetimes. The 1 Π u state is repulsive, but the chemical bonding causes an inflection to appear in the potential curve.

Theoretical study of the spectroscopy of Al2

The singlet and triplet states of Al2 below about 30 000 cm−1 have been studied at the multireference configuration‐interaction level in a [8s 7p 5d 2f] Gaussian basis. We attempt to identify and characterize the band systems in both the singlet and triplet manifolds that should be most amenable to experimental study. The spectroscopy of Al2 can be understood in terms of an X 3Πu ground state, and except for the well known (1)3Σ−u–A 3Σ−g emission system, all other transitions that we can unambiguously assign involve the X 3Πu ground state. Above about 27 000 cm−1 the spectrum of Al2 is complicated by the presence of several overlapping transitions. The calculations suggest that the assignments of the E and F systems observed recently in a jet‐cooled beam are correct, although the considerable remaining differences between the experimental and theoretical spectroscopic constants and radiative lifetimes preclude a definitive assignment. The very intense E’ system observed by Morse is assigned to the (3)3Πg–...

On the bonding of La+ and La2+ to C2H2, C2H4, and C3H6

Abstract The interaction of La+ and La2+ with C2H2, C2H4, and C3H6 is studied using electronic structure calculations that include correlation. The calculations show that the bonding in the dication is electrostatic in origin, and the computed binding energies are in good agreement with experiment. The La+ forms two chemical bonds with the hydrocarbons. Since the π bond is weaker for C2H2 than C2H4, the La+C2H2 binding energy is larger than for La+C2H4. LaC3H6+ rearranges to yield a stronger bond than in LaC2H4+ even though both hydrocarbons have a double bond.

Addendum to on the bonding in Be22

The lowest excited state of Be22+ is 1Σu+, not 1Πu (as stated by the authors in a recent Letter). This state is metastable, supporting at least four vibrational levels with appreciable lifetimes. The bond length of the 1Σu+ state is significantly longer than the 1Σg+ ground state, leading to small Franck—Condon factors for the absorption from the lowest vibrational level of the ground state.

The photoelectron spectroscopy of ZnCl2

Abstract We report the ionization energies (IEs) corresponding to the Cl ligand electrons and the Zn 3d electrons in ZnCl 2 computed using large Gaussian basis sets and a high level of correlation treatment. The IEs for the CI ligand electrons are in excellent agreement with those determined from photoelectron spectra. The IEs corresponding to the Zn 3d electrons agree with experiment relatively well in absolute magnitude, but differ in order. The vibrational frequencies of the ground state agree very well with experiment, and predictions are made for the corresponding frequencies in the positive ion. We observe symmetry breaking for the 2 Π g and 2 Σ u + electronic states of ZnCl 2 + to give an asymmetric geometry [Cl…ZnCl] + .