Enhancement of the absorption bands in the infrared spectra of low-temperature uracil films by interference

An experimental method that enables significant enhancement of the bands in the IR absorption spectra of low-temperature films, using standard equipment for matrix isolation, was proposed. The effect is achieved due to the interference amplification of an electromagnetic wave using a sublayer of Ar film. IR Fourier spectra of low-temperature films of uracil (Ur) molecules were obtained in the range of 2000-500 cm(-1), with a resolution of 3 cm(-1). Thin Ur films with thickness of approximately 0.3 mu m were grown at low temperatures on the surface of argon films of thickness of 2.3 and 1.1 mu m. An enhancement in the spectral range of 1250-500 cm(-1) was recorded for the first bilayer structure, and in the range of 2000-500 cm(-1) for the second one. As a result of amplification in the spectrum of the low-temperature uracil film, absorption bands in the range of out-of-plane deformation vibrations of 1000-500 cm(-1) were recorded for the first time. It was found that the out-of-plane fundamental NH modes of Ur groups are most sensitive to changes in the crystal structure of the film. It was shown that the absorption spectrum of the Ur film heated to room temperature differs from the spectrum of the Ur crystal obtained from the solution, which indicates a difference in their structures. Published by AIP Publishing.