This work solves the long-standing conundrum of the correct experimental value for the second hyperpolarizability of CS₂ vapor (γ^CS₂). Hyperpolarizabilities are the source of the generation of multiple harmonics of the frequency of a driving laser field. The cumulated effect for small molecules in vapor is small, thus the accurate measurement of hyperpolarizabilities is difficult. Conversely, accurate theoretical calculations of all electronic and vibrational contributions to hyperpolarizabilities are easier for smaller molecules. Unfortunately, even the most accurate calculations of γ^CS₂ deviate strongly from measurements performed in the 1970s, but are in agreement with recent measurements, all of them performed at a single input frequency. Using a phase-matching technique and tunable lasers, Fernandez and Shelton measured γ^CS₂ accurately over a large frequency interval. They obtained results up to ten times smaller than the older measurements, in agreement with the newer ones. The results are also generally in agreement with theoretical calculations, which differ by 20% among each other. The dispersion curve in particular matches nicely the theoretical curve obtained at the surprisingly low computational level of uncorrelated time-dependent Hartree-Fock theory, if corrected by a small vibrational contribution. Thus, CS₂ may become a new reference standard for hyperpolarizability measurements in vapor, if the results are confirmed independently, e.g. by new theoretical high-level calculations.

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