A theoretical study of C n Cl, C n Cl + , and C n Cl − (n = 1-7) clusters has been carried out. Predictions for their electronic structures, dipole moments, and vibrational frequencies have been made at the B3LYP/6-311G(d) level. According to our calculations the lowest-lying geometry of all these species (with the only exception of neutral C 3 Cl) is predicted to be either a linear or quasi-linear structure with chlorine located at the end of the carbon chain. C n Cl clusters all have doublet ground states, whereas the anionic clusters, with the only exception of CCl − , all have singlet ground states. For C n Cl + species, n-even clusters have triplet ground states whereas n-odd ones have singlet ground states. An even-odd parity effect (n-even clusters more stable than n-odd ones) is found for both the neutral and anionic species, whereas in the case of the cations the alternation in stability is reversed. The ionization potential (IP) and electron affinity (EA) also exhibit regular variations with the size of the cluster, with n-even clusters having both higher IP and EA than n-odd ones.

Cyanides and isocyanides of first-row transition metal M(CN) (M=Sc-Zn) are investigated with quantum chemistry techniques, providing predictions for their molecular properties. A careful analysis of the competition between cyanide and isocyanide isomers along the transition series has been carried out. In agreement with the experimental observations, late transition metals (Co-Zn) clearly prefer a cyanide arrangement. On the other hand, early transition metals (Sc-Fe), with the only exception of the Cr(CN) system, favor the isocyanide isomer. The theoretical calculations predict the following unknown isocyanides, ScNC(3Delta), TiNC(4Phi), VNC(5Delta), and MnNC(7Sigma+), and agree with the experimental observation of FeNC(6Delta) and the CrCN(6Sigma+) cyanide. First-row transition metal cyanides and isocyanides are predicted to have relatively large dissociation energies with values within the range 80-101 kcal mol(-1), except Zn(CN), which has a dissociation energy around 50-55 kcal mol(-1), and low isomerization barriers. A detailed analysis of the bonding has been carried out employing the topological analysis of the charge density and an energy decomposition analysis. The role of the covalent and electrostatic contributions to the metal-ligand bonding, as well as the importance of pi bonding, are discussed.

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AlC n , AlC n + , and AlC n -(n ) 1-7) clusters have been studied by means of the B3LYP density functional method. Results of their equilibrium geometries, electronic energies, dipole moments, and vibrational frequencies are reported. The energy calculations show that the open-chain linear or quasi-linear isomers with the aluminum atom bound to the end of the carbon chain are the most stable geometry in all cases. For the AlC n clusters the electronic structure is predicted to be a doublet, with the only exception of AlC. In the AlC n + species, the electronic ground state was found to be alternately a singlet for odd n or a triplet for even n, again with the exception of the first member of the series, and in the AlC nclusters the opposite was found. From the binding energies we can deduce an even-odd parity effect, with n-even clustering atoms being more stable than those with odd ones in the neutral and anionic clusters, whereas in the cations this effect is reversed. The ionization potentials (IP) and electron affinities (EA) also computed show an evenodd alternation with n-even clusters presenting both higher IP and EA than n-odd ones.

We study the viability of different gas-phase ion-molecule reactions that could produce precursors of formamide in the interstellar medium. We analyze different reactions between cations containing a nitrogen atom (NH + 3 , NH + 4 , NH 3 OH + , and NH 2 OH + ) and neutral molecules having one carbonyl group (H 2 CO and HCOOH). First, we report a theoretical estimation of the reaction enthalpies for the proposed processes. Second, for more favorable reactions, from a thermodynamic point of view, we perform a theoretical study of the potential energy surface. In particular, the more exothermic processes correspond to the reactions of ionized and protonated hydroxylamine with formaldehyde. In addition, a neutral-neutral reaction has also been considered. The analysis of the potential energy surfaces corresponding to these reactions shows that these processes present a net activation barrier and that they cannot be considered as a source of formamide in space.