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The infra-red spectra of melamine and of melamine-& have been studied from 450 to 5000 cm-1 in the solid state. The spectral studies support the view that the molecule has the almost all-planar cyanuric triamide structure in the crystal state.A complete frequency assignment is attempted for the class Ai, class A: and class E' vibrations. The splitting of the absorption bands arising from the doubly-degenerate class E' modes and the appearance of the infra-red forbidden class Ai absorptions is interpreted as evidence that the molecule is distorted in the crystal thus losing to some extent its D3h symmetry.

Experimentally a large number of linear relations have been found between the change in OH stretching frequency, Av, on hydrogen bonding and the hydrogen bond energy, AH. A least square treatment of these A< against AH relations is carried out for constant acceptor, variable donor as well as constant donor, variable acceptor systems. Generally, the constant-acceptor plots have much higher values of intercepts than the constant-donor plots. The slopes of the constant-donor plots seem to vary with the basicity of the donor. However, since 4i should go to zero when there is no interaction, it is suggested that the complete 4 v against 4 H relation could be nonlinear. Molecular orbital calculations have been employed to throw light on the A< against AH relation. It is also shown that charge transfer theory when applied to the hydrogen bond predicts a relation between A H and the quantity where Go and V are the free and perturbed OH stretching frequencies.

Raman spectra of ethylene trapped in argon matrices are compared with the corresponding infrared data. Bands due to monomer and dimer species could be distinguished by their concentration dependence. Possible structures of the dimer are discussed.

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