Knowledge Bank

The vibration-rotation band $\sigma 2$ of $NO2$ originally observed prismatically by Bailey and $Cassie1$ and by $Schaffert2$ has been reexamined with a 1200 lines-per-inch grating. The sample was contained in a 10-cm monel cell closed with silver chloride windows at a temperature of $175\circ C$ and a pressure of 45 cm of mercury. This band extends from about 650 K to 900 K and consists of lines which vary in separation from about 9 K at the low-wave-number end to 19 K at the high-wave-number end. It was necessary to record at high temperature because the central region of the band is completely obscured by a band of $N2O4$, with which $NO2$ exists in equilibrium at ordinary temperature. The band has the appearance of a perpendicular band for a symmetric top, with the exception that the convergence of the lines is not uniform. The convergence is interrupted at the band center by the abnormal spacing of , , , . and are unsymmetrical in form, shade off toward high wave numbers, and appear to be too close together. and shade off toward low wave numbers and are too close together. The central pair and are too far apart. A band analysis carried out with symmetric top assumptions and neglecting the four central lines gives a band center of $749.65K$ and $\Delta (A-B)$ of 0.337 K. This band center differs by 1.2 K from the value 750.9 K quoted by Moore . Rotational constants obtained from this analysis are ($A\prime \prime -B\prime \prime )=7.583K$, and $(A\prime -B\prime )=7.923K$. The difference between these numbers, 0.340 K, is in good agreement with the slope of the band center graph quoted above. A value of $DK\prime =DK\prime \prime 2.59\times 10-3K$ may be obtained as the slope of the $(A-B)$ graphs. This is about one-half the value quoted by $Moore3$.