A set of potential energy constants has been obtained for CH3I and CD3I from their vibrational spectral data. From these constants, the rotational distortion constants and the mean amplitudes have been calculated for these two molecules. The rotational distortion constants DJ, DJK, and DK were, respectively, CH3I, 6.34, 59.36, and 3 542.30; CD3I, 3.90, 33.08, and 866.43 kc/s. The principal mean amplitudes of vibration in pm (pm = picometer = 10−12 meter = 10−2 Å) at 298.16°K are CH3I, 5.25 (C—I), 7.71 (C—H), 12.37 [Formula: see text], and 12.00 [Formula: see text]; CD3I, 5.14 (C—I), 6.63 (C—D), 10.85 [Formula: see text], and 10.65 [Formula: see text]. The potential energy constants were used to obtain the wave numbers of CH2DI and CD2HI. A complete assignment of the observed wave numbers for the molecules CH2DI and CD2HI has been made. The fundamental wave numbers for the gaseous state of CH2DI are a′, 2 980, 2 235, 1 418, 1 170, 723, and 519; a″, 3 091, 1 266, and 871 cycles/cm. For CD2HI, the corresponding values are a′, 3 017, 2 174, 1 185, 1 009, 757, and 508; a″, 2 273, 1 279, and 676. With these wave numbers, the thermodynamic functions have been calculated for the two molecules for 12 temperatures from 100 to 1 000°K for 1 atm pressure. The values of (H0−E00)/T, −(F0−E00)/T, S0, and Cp0 at 298.16°K are, respectively, CH2DI, 8.82, 54.66, 63.48, and 10.98; CD2HI, 9.00, 55.20, 64.19, and 11.53 cal deg−1 mole−1.
