Mössbauer studies of matrix-isolated Sn, Sn2and 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.

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