Dilute solid solutions of 14N2, 15N2, and CO in Ar at helium temperatures: heat capacities and rotational spectra of impurity molecules

Heat capacities of dilute solid solutions of 15N2 and CO in Ar are studied in the temperature range from 0.5 to 6 K for impurity concentrations n ≥ 0.25 mol.%. The obtained results are considered together with the available data on heat capacity of dilute solutions of 14N2 in Ar. An energy spectrum of retarded rotational motion of isolated N2 and CO molecules in solid argon is proposed.