Specific Heat of Carbon Dioxide at Low Temperatures

Abstract

A NEW Raman line with Δν = 58 cm.^-1 was observed by us¹ in the Raman spectrum of solid carbon dioxide at — 80° C. Since the heat capacities of solid carbon dioxide at low temperatures are known², it may be of interest to examine whether these values agree with those obtained from a corresponding Debye function. If the value of Δ ν of the observed new line be taken as 63 cm.^-1, in view of the fact that this value increases slightly at low temperatures in other cases, the value of hν/k is 90·3°. If the line be due to lattice oscillation, the values of C_v should be given by the corresponding Debye function with three degrees of freedom, because the crystal being cubic, ν has the same value for the three degrees of freedom. The calculated values are given in the second column of the accompanying table, and the observed values of C_p are given in the last column. It can be seen that the former are much greater than the latter at low temperatures. This shows that the new line is not due to a lattice oscillation involving translational motions of the molecules.