The vibrational spectrum and rotational constants of difluoroethyne FC 3/4 CF. Matrix and high resolution infrared studies and a b i n i t i o calculations

Abstract

Infrared spectra of the short-lived difluoroethyne molecule have been recorded in neon and argon matrices between 200 and 5000 cm−1. Fourier transform infrared spectra with a resolution of 0.004 cm−1 have been measured in the gas phase around 1350 cm−1 (ν3, ν2+ν4+ν5, hot bands) and 2150 cm−1 (ν2+ν3, ν1−ν5, hot bands). The high resolution study yields rotational parameters of the ground and all singly excited vibrational states. The interpretation of the experimental data has been guided by ab initio calculations at the SCF (self-consistent-field) level and the correlated MP2 level (Moller–Plesset second order perturbation theory) employing three different large basis sets. The theoretical calculations provide the SCF and MP2 harmonic fields as well as the SCF anharmonic force field of FCCF. The agreement between the available theoretical and experimental results is generally quite good, with the exception of the spectroscopic constants involving the trans-bending mode ν4 where more theoretical work is required. The combined use of theoretical and experimental information leads to an estimate of the equilibrium structure [D∞h, re(CC)=1.1865 Å, re(CF)=1.2832 Å] and to recommended ‘‘best’’ values for the wave numbers of all fundamental vibrations based on the matrix and high resolution infrared data and some ab initio anharmonicity constants. The present study demonstrates the advantages of a combined theoretical and experimental approach to the spectroscopy of short-lived molecules.

Equilibrium Structure and Spectroscopic Constants of Difluoroethyne: An ab Initio Study

“…Based on the combined use of theoretical and ex-Plesset perturbation theory (MP2) (11), coupled cluster theory with single and double excitations (12) augmented by perimental information the equilibrium bond lengths of FCCF have been estimated as r e (CC) Å 1.1865 Å and r e a perturbational estimate of the effects of connected triple excitations (CCSD(T)) (13), and multiconfigurational sec-(CF) Å 1.2832 Å (1). More recently, a purely experimental determination of the equilibrium geometry has been at-ond-order perturbation theory (CASPT2) (14, 15), including also the nondiagonal elements of the Fock matrix in tempted (5) employing the observed equilibrium rotational constant B e of F 12 C 12 CF (1) and an estimated B e value of the zeroth-order Hamiltonian (15). These calculations were performed with the GAUSSIAN92 (16), ACES II (17), F 12 C 13 CF which has been derived from the observed B 0 value (5) by an empirical correction (6).…”

“…led to r e (CC) Å 1.1973 (30) Å and r e (CF) Å 1.2767 (15) Å . Obviously, there is a significant deviation between these Three different basis sets were employed: TZ2Pf is a valence triple zeta plus double polarization plus f function published equilibrium structures (1,5) which has motivated the present investigation.…”

“…Quantum-chemical calculations were carried out at the The unstable, short-lived difluoroethyne molecule has been studied by matrix (1) and high-resolution gas-phase Hartree-Fock self-consistent field (SCF) level of theory (10) and at the correlated levels of second-order Møller-infrared spectroscopy (1)(2)(3)(4). It has a centrosymmetric linear structure.…”

The High-Resolution FTIR Far-Infrared Spectrum of Formamide

“…Using high-level ab initio molecular orbital calculations, quadratic, cubic, and quartic force fields for linear molecules such as FCCF (30) and FCCC1 (31) can be found. The rovibrational parameters derived from these force fields can be used to guide analysis of high-resolution FTIR data.…”

The Diversity of Difluoroacetylene Coordination Modes Obtained by Coupling Fluorocarbyne Ligands on Binuclear Manganese Carbonyl Sites

“…The C-C distance of the C 2 F 2 ligand in 27-2 of 1.415 (B3LYP) or 1.438 (BP86) suggests a short single bond, thus indicating that this bridging C 2 F 2 ligand is a biscarbene ligand that also donates two electrons to each metal atom, similar to the C 2 F 2 ligand in 27-1. For comparison, the C C triple bond length in free difluoroacetylene has been estimated at 1.186 from the high-resolution infrared spectrum [42,43] and from high-level CCSD(T)/cc-pVQZ calculations. [44] The presence of a four-electron donor bridging carbonyl group in 27-2 means that only a Mn À Mn single bond is necessary to give both manganese atoms in 27-2 the favored 18-electron configuration.…”