Knowledge Bank

Recent results have been obtained in the analysis of vibration-rotation spectra of light $XY4$ molecules, using a new tetrahedral formalism developed in the DIJON $Laboratory1$. Two main results are reported: -(i) Treatment of interacting fundamentals ($\nu 4$ and $\nu 4$ of $CH4$ and $SiH4$; $\nu 1$ and $\nu 3$ of $SiH4$) with an untransformed third-order Hamiltonian. A reduced set of parameters given better results than previous fourth order theories. -(ii) Analysis of harmonic and combination bands by a systematic extrapolation from the corresponding fundamental: $2\nu 2,2\nu 4,\nu 2,+\nu 4$ and $\nu 2+\nu 3$ of methane. As a consequence, a first set of anharmonic constants have been obtained. Several works in progress are briefly discussed: -(i) Treatment of interacting vibrational clusters. (The pentade $\nu 1-\nu 3-2\nu 2-2\nu 4-\nu 2+\nu 4$ of $CH4$). -(ii) Computation of hot bands. -(iii) Analysis of levels involving more than two vibrational quanta.