In the vibrational spectrum of the ${\mathrm{CS}}_2$ molecule, a clear transition in the "staircase" function $N\left(E\right)\mathrm{}$ has been observed for the first time at $E_c\sim 13 000$ ${\mathrm{cm}}^{-1\mathrm{}}$. The analysis for spectral correlations over short and large distances shows that this transition could be associated with a transition towards a classically chaotic regime. A vibrational spectrum of high quality has been obtained of the ${\mathrm{CS}}_2$ molecule in its fundamental electronic state. This spectrum of a single symmetry shows 966 purely vibrational levels ($J^{\prime \prime }=0\mathrm{}$) up to 19 200 ${\mathrm{cm}}^{-1\mathrm{}}$. The absolute precision of the measured position of the levels is 0.05 ${\mathrm{cm}}^{-1\mathrm{}}$, and the dynamic intensity range is greater than 5000.

• Received 25 January 1994

DOI:https://doi.org/10.1103/PhysRevLett.73.232