Knowledge Bank

The bands of the triad $2\nu 1+\nu 3,\nu 1+2\nu 2+\nu 3,4\nu 2+\nu 3$ and of the tetrad $3\nu 1+\nu 3,2\nu 1+2\nu 2+\nu 3,\nu 1+4\nu 2+\nu 3,6\nu 2+\nu 3$ have been reinvestigated with a long absorbing path and high resolution. A greater number of lines than previously observed have been measured making it possible to obtain better rotational constants B and D. The centrifugal distortion constants D obtained for the upper states of the bands differ from that of the ground state by amounts up to 50%. This effect appears to be symmetric within the triad and within the tetrad, and the mean value of the constants D for each of these groups of levels is nearly the same as the value in the ground state. A similar effect has also been observed in some of the corresponding ""hot"" bands, e.g., $5\nu 2+\nu 3-\nu 2$.