A theoretical study of SnF2+, SnCl2+, and SnO2+ and their experimental search

Abstract

We present a detailed theoretical study of the stability of the gas-phase diatomic dications SnF(2+), SnCl(2+), and SnO(2+) using ab initio computer calculations. The ground states of SnF(2+), SnCl(2+), and SnO(2+) are thermodynamically stable, respectively, with dissociation energies of 0.45, 0.30, and 0.42 eV. Whereas SnF(2+) dissociates into Sn(2+) + F, the long range behaviour of the potential energy curves of SnCl(2+) and SnO(2+) is repulsive and wide barrier heights due to avoided crossing act as a kind of effective dissociation energy. Their equilibrium internuclear distances are 4.855, 5.201, and 4.852 a(0), respectively. The double ionisation energies (T(e)) to form SnF(2+), SnCl(2+), and SnO(2+) from their respective neutral parents are 25.87, 23.71, and 25.97 eV. We combine our theoretical work with the experimental results of a search for these doubly positively charged diatomic molecules in the gas phase. SnO(2+) and SnF(2+) have been observed for prolonged oxygen ((16)O(-)) ion beam sputtering of a tin metal foil and of tin (II) fluoride (SnF(2)) powder, respectively, for ion flight times of about 10(-5) s through a magnetic-sector mass spectrometer. In addition, SnCl(2+) has been detected for (16)O(-) ion surface bombardment of stannous (tin (II)) chloride (SnCl(2)) powder. To our knowledge, SnF(2+) is a novel gas-phase molecule, whereas SnCl(2+) had been detected previously by electron-impact ionization mass spectrometry, and SnO(2+) had been observed before by spark source mass spectrometry as well as by atom probe mass spectrometry. We are not aware of any previous theoretical studies of these molecular systems.

Multireference Approaches for Excited States of Molecules

“…For diatomic molecules involving light atoms up to Ar, the characterization of the electronic structure and the spectroscopic parameters of the ground and excited states is well established by the use of multireference methodologies. These approaches have successfully predicted the properties of the ground and excited electronic states for the main group elements investigated lately. − Most of these studies were carried out using the internally contracted MRCI ( ic -MRCI, see section ). Sivalingam et al have compared the performance of this method for the ground and excited states of selected diatomic molecules with the strongly contracted MRCI (SC-MRCI) method, showing that the two methods are bounded from below by the uncontracted MRCI ( uc -MRCI).…”

How To Arrive at Accurate Benchmark Values for Transition Metal Compounds: Computation or Experiment?

“…The single-reference CC hierarchy breaks down whenever a single determinant becomes an improper zeroth-order description of the system, whereas multireference methods lack a systematic hierarchy comparable to CC theory. The standard schemes, beyond second-order perturbation theory, still rely on multireference configuration interaction (MRCI) with approximate size-extensivity corrections. − The extension of coupled-cluster theory to multireference cases, on the other hand, is not straightforward, and only recently have a number of implementations been reported that are capable of treating realistic systems. − In this context, the multireference coupled-cluster (MRCC) theory , should provide a very reliable way to treat systems with such complex electronic structure.…”