YH3 and YD3: Heat Capacities and Thermodynamic Functions from 15° to 350°K and Infrared Absorption Spectra

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Abstract
The heat capacities of YH3 and YD3 were determined in an adiabatic calorimeter from 15° to 350°K. The heat capacity, entropy, enthalpy, and Gibbs free‐energy function for YH3 at 298.15°K are 10.363±0.021 cal deg—1 mole—1, 10.019±0.020 cal deg—1 mole—1, 1613.3±3.2 cal mole—1, and —4.608±0.009 cal deg—1 mole—1, respectively. The corresponding quantities for YD3 are 13.727±0.028, 12.028±0.024, 2024.8±4.0, and —5.237±0.010. The infrared absorption spectra of YH3 and YD3 were taken in the range 400 to 4000 cm—1. Maxima in the absorption bands of YH3 were observed at 1295, 920, and 640 cm—1 and in the absorption bands of YD3 at 1295/√2, 920/√2, and 640/√2 cm—1. A reasonable assignment of these frequencies to Y—H and Y—D vibrations satisfactorily accounts for the difference between the heat capacities of YH3 and YD3 in the temperature range 50° to 350°K. The lattice parameters as determined by x‐ray diffraction for the hexagonal close‐packed trihydrides were a0 = 3.672±0.002 Å and c0 = 6.625±0.018 Å for YH3 and a0 = 3.659±0.002 Å and c0 = 6.586±0.019 Å for YD3.