Knowledge Bank

The infrared spectrum of single crystals of sodium and lithium nitrate has been observed as a function of temperature, pressure, polarization, direction of propagation, sample size, and isotopic composition. An interpretation of the structure and dependence on direction of propagation of the very intense $\nu 3$ absorption is offered. An assignment of the rich multiphonon spectrum based on the observed isotope shifts is suggested and the pressure dependence of the fundamental frequencies is discussed in terms of a dipolar coupling model.