Characterisation of monomeric methylsodium and methylpotassium: infrared spectra of the matrix-isolated molecules

Abstract

Co-condensation of CH3l with sodium or potassium vapour and an excess of N2 at ca. 20 K gives rise to the respective methylmetal monomer CH3Na or CH3K which is trapped in the resulting matrix. The i.r. spectrum of the matrix in the region 200–4 000 cm–1 discloses all six vibrational fundamentals characterising each of these molecules in C3v symmetry, the assignments being verified by measurements taking in the fully deuteriated as well as the undeuteriated isotopomer. How closely the molecules approximate to the formulation of CH3–M+(M = Na or K) is revealed through fundamentals which are lower in energy than those of any other homoleptic methylmetal compound reported to date. Normal co-ordinate analysis underlines this aspect with M–C stretching force constants =ca. 48 N m–1 and CH3 rocking force constants = 10.3 (M = Na) and 7.6 N m rad–2(M = K) which set new standards by their diminutive values.