Mössbauer studies of matrix-isolated Sn, Sn2 and higher polymers and their diffusion behaviour in solid nitrogen

Abstract

The Mössbauer parameters of nitrogen-isolated tin dimers (isomer shift δ at 4.2 K = 3.2 mm s^–1, quadrupole splitting Δ= 3.6 mm s^–1) and tin polymers (δ= 3.0 mm s^–1, Δ= 2.0 mm s^–1) have been established and those of tin monomers (δ= 3.22 mm s^–1, Δ= 0.6 mm s^–1) measured between 1.5 and 14.9 K. The f factors of all the species are approximately 0.4. The effective Debye temperature of the monomers of 48 K is slightly higher than that predicted from the mass-defect model. Although the monomers interacted sufficiently strongly with the surrounding nitrogen molecules to produce the quadrupole splitting, no nitrogen stretching frequencies were observed in the infra-red spectrum. The parameters of the dimer were consistent with a singlet ground state of the molecule. The diffusion coefficient of the monomer is 3 × 10^–22 m² s^–1 in α–N₂ at 34 K, and is greater than 10^–20 m²s^–1 in β–N₂ at 36 K. Comparison with estimated rates of self-diffusion in α–N₂ showed that the monomer mobility was not greatly different from that of nitrogen molecules themselves. At higher temperatures the dimers and polymers combined to give small particles (δ= 2.55 mm s^–1) of β–Sn.