Knowledge Bank

The infrared-active $\ell =1$ band of the $3\nu 3$ manifold has been recorded at T=160 K with Doppler-limited resolution using a tunable laser difference-frequency spectrometer. Most of the principal structure in the $\ell =1P,O$, and R branches have been identified along with some overlapping structure in the weak $\ell =3$ band. About 180 lines with $J\le 30$ have been fitted with a model Hamiltonian which allows the $\ell =1$ and $\zeta =3$ bands to Interact. The derived spectroscopic constants are in agreement with those of $\upsilon 3$. The three anharmonic coefficients $X33,G33$, and $T33$ have been accurately determined so that the vibrational levels in the $n\upsilon 3$ ladder can be predicted accurately for several values of n.