Knowledge Bank

“The infrared spectra of $N14O2$ and $N15O2$ were observed under high dispersion with gas pressures up to 15 cm of $N14O2$ and 4 cm of $N15O2$ in a 20 meter absorption cell. Ten bands of $N15O2$, eight with well-resolved rotation lines; and nine bands of $N15O2$, seven with well-resolved rotation lines, were observed. The band centers of these bands were determined, from which all the $\omega i$ and $xij$ were calculated. By making use of the very good assumption that the potential constants are the same for isotopic molecules, the four force constants in the most general quadratic potential function were found to be $fd=10.927\pm .065,f\alpha =1.125\pm .003,fdd=2.038\pm .65,andfda=.390=.020$ (all in millidynes/\AA). The following ground state rotational constants were obtained from the rotational structures of the observed bands using symmetric top combination relations: for $N14O2;A=8.003,B=.434,C=A12$; and for $N15O2,A=7.642,B=.434,C=.410$ (all in $cm-1$). Theoretical spectra, calculated for type A and type B bands by subsituting these rotational constants into the asymmetric top equations gave excellent agreement when compared with the observed spectra. The partition function ratio for $N15O2$ to $N14O2$ is found to be 1.1080 at $25\circ C$.”