INFRARED SPECTRAL DATA, ROTATIONAL CONSTANTS, AND THERMODYNAMIC PROPERTIES FOR $CD_{3}Br$ AND $CH_{3}Br$

Abstract

Infrared spectra were obtained between 400 and 4000 K with NaCl and KBr prisms. The $a_{1}$ fundamentals for $CD_{3}Br$ are 2157, 993, and 578 K; for $CH_{3}Br$ they are 2972, 1305, and 611 K. For $CD_{3}Br$, a least squares analysis of the observed wave numbers of the sub-bands of $\sigma_{6}$(e) gave for $B_{1}$, $A_{1}$, $\zeta$, and $\sigma_{0}$ the values 0.255, 2.529, 0.150, and 712.3K; for $\sigma_{5}$(e) the values were $0.257, 2.530, -0.339$, and $1056.2$. For $\sigma_{4}$(e) $- 2293 K$, the sub-bands were not resolved, but the sum rule gave $\zeta_{4} = 0.240$. The signs of $B_{1}-B_{0}$ for $\sigma_{6}$ and $\sigma_{5}$ are the same as those previously obtained for $CH_{3}I$ by use of the high-dispersion records of Lagemann and Nielsen. For $CH_{3}Br$, a least squares analysis of the grating data of Bennett and Meyer gave for $\sigma_{6}$(e): 0.315, 5.144, 0.217, and 955.4; for $\sigma_{5}$(e): $0.304, 5.062, -0.242$, and $1448.2$; and for $\sigma_{4}$(e): $0.321, 5.153, 0.064$, and $3055.6$. The sign of $B_{1}-B_{0}$ for $\sigma_{6}$ is the same as for $CH_{3}I$, but the signs for $\sigma_{5}$ and $\sigma_{4}$ are reversed. This inconsistency is presumably due to the limited accuracy with which the two small constants $B_{1}-B_{0}$ and ($A_{1}-B_{1})-(A_{0}-B_{0}$) can be determined by the least squares method. The microwave value of $B_{0}$ was used. For $CD_{3}Br$, the values of ($H^{0}-E_{0}^{0})/T, - (F^{0}-E_{0}^{0})/T, S^{0}$ and $C_{p}^{0}$ at $100^{0}, 273.16^{0}, 298.16^{0}, 900^{0}$, and $1550^{0}$ K are respectively: 7.95, 42.62, 50.58, 8.00; 8.75, 49.96, 58.77, 10.66; 8.98, 51.65, 60.63, 11.69; 14.24, 64.07, 78.31, 20.39; and 17.57, 72.01, 90.21, 23.44 cal $deg^{-1}$ $mole^{-1}$. For $CH_{3}Br$, the corresponding values are: 7.95, 41.40, 49.35, 7.98; 8.37, 48.69, 57.06, 9.72; 8.51, 50.24, 58.75, 10.15; 12.64, 61.41, 74.05, 18.20; and 15.87, 69.24, 85.11, 22.00. Values for 27 other temperatures in this range were calculated.