Knowledge Bank

Infrared spectra were obtained between 400 and 4000 K with NaCl and KBr prisms. The $a1$ fundamentals for $CD3Br$ are 2157, 993, and 578 K; for $CH3Br$ they are 2972, 1305, and 611 K. For $CD3Br$, a least squares analysis of the observed wave numbers of the sub-bands of $\sigma 6$(e) gave for $B1$, $A1$, $\zeta$, 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) $-2293K$, the sub-bands were not resolved, but the sum rule gave $\zeta 4=0.240$. The signs of $B1-B0$ for $\sigma 6$ and $\sigma 5$ are the same as those previously obtained for $CH3I$ by use of the high-dispersion records of Lagemann and Nielsen. For $CH3Br$, 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 $B1-B0$ for $\sigma 6$ is the same as for $CH3I$, 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 $B1-B0$ and ($A1-B1)-(A0-B0$) can be determined by the least squares method. The microwave value of $B0$ was used. For $CD3Br$, the values of ($H0-E00)/T,-(F0-E00)/T,S0$ and $Cp0$ at $1000,273.160,298.160,9000$, and $15500$ 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 $CH3Br$, 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.