ESR of Cu(NO3)2 and CuF2 Molecules Oriented in Neon and Argon Matrices at 4°K

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Abstract
An experimental apparatus is described which allows the trapping of preferentially oriented molecules in neon and argon matrices at 4°K and the measurement of their ESR spectra at various orientations relative to the magnetic field. Application to Cu(NO3)2, vaporizing at 150°C, and CuF2, vaporizing at 925°C, demonstrates that the degree of orientation is dependent upon the temperature of the vaporizing molecule and the matrix gas used. The ESR spectra of highly oriented Cu(NO3)2 in neon at 4°K (there was essentially no orientation in argon) indicate that the molecule is planar with the four nitrate oxygen atoms surrounding the Cu++ ion in a square array. The g and A values are very similar to those found in copper chelate molecules: g∥ = 2.2489±0.003, g⊥ = 2.0522±0.0005, A∥ (63Cu) = 570±3 Mc/sec, and A⊥ (63Cu) = 50±3 Mc/sec. Computer simulation of the spectra not only confirms this assignment but provides an estimate of the degree of orientation as a function of the inclination. CuF2 isolated in argon at 4°K has been found to be highly oriented also. Its ESR assignment supports the view that the molecule is linear with magnetic parameters g∥ = 1.913±0.001, g⊥ = 2.601±0.001, A∥ (63Cu) = 1933±5 Mc/sec, A⊥ (63Cu) = 2090±5 Mc/sec, A∥ (F) = 308±1 Mc/sec, and A⊥ (F) = 206±1 Mc/sec. The unusually large hyperfine interaction with the Cu nucleus indicates a substantial admixture of its 4s orbital. For both molecules the assignments were greatly facilitated by the partial orientation of the molecules in the matrices. The optical spectra of CuF2 in neon at 4°K yielded the asymmetric stretching frequency at 769 cm−1. No absorption bands were found between 8900 and 3300 Å.