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The hyperpolarizabilities γ of CH4, CF4, and SF6 were measured by the dc Kerr effect at wavelengths from 457.9 to 1092 nm. Vibrational hyperpolarizabilities γv were obtained by combining these measurements with electric-field-induced second harmonic generation (ESHG) measurements. The vibrational contribution to the hyperpolarizability ranges from 6% to 35% of the total. At high optical frequency the difference between γv for Kerr and γv for ESHG is approximately constant, and has values 18, 31, and 51×10-63 C4 m4 J-3 for CH4, CF4, and SF6, respectively. The experimental results are in good quantitative agreement with the results of recent ab initio calculations of the frequency dependence of γv for CH4, except for a small but non-negligible discrepancy at high frequency. © 1996 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The Raman spectra of the vibrational fundamental, first overtone and second overtone transitions of the H2 molecule were recorded using visible and ultraviolet argon–ion laser excitation. The ratios of transition polarizability matrix elements, α01,21/α01,11 and α01,31/α01,11, were determined from the measured intensities of the Q(1) Raman lines v,J=0,1→v’,1 for v’=1,2,3. The experimentally determined value of the Raman first overtone matrix element is in good agreement with the value from the best ab initio calculation. [ABSTRACT FROM AUTHOR]

Expressions are derived for the vibrational second hyperpolarizability γv of SF6, in the static limit and for the nonlinear-optical processes of the dc Kerr effect, electric-field-induced second harmonic generation (ESHG), and third harmonic generation (THG). These expressions give γv in terms of vibrational transition dipole, polarizability, and first hyperpolarizability matrix elements (μ,α,β). The matrix elements needed in the numerical evaluation of γv are obtained from the literature and from the Raman scattering measurements reported here. In the static limit it is found that γvapprox. 20 γe, where γe is the electronic contribution to γ. At optical frequencies γv is still comparable to γe in magnitude, and it shows significant frequency dependence. [ABSTRACT FROM AUTHOR]

The frequency dependence of the second hyperpolarizability (γ) of CF4 has been measured in the visible (488 nm<λ<660 nm) by means of gas-phase electric-field-induced second harmonic generation (ESHG). The results of these experiments are compared with the results of other nonlinear optics experiments which have measured γ by third harmonic generation (THG), ESHG, and the dc Kerr effect. In order to make this comparison, expressions for the vibrational contributions to γCF4 have been derived and numerically evaluated for each of these optical processes. This comparison indicates that vibrational contributions to γCF4 are significant for both the dc Kerr effect and ESHG. [ABSTRACT FROM AUTHOR]

The frequency dependence of the second hyperpolarizability (γ) of CO2 has been measured in the visible (488<λ<693 nm) by means of gas phase electric-field-induced second-harmonic generation (ESHG). Comparison of these results with the results for several other third-order nonlinear optical processes suggests that there are significant vibrational contributions to γCO2. [ABSTRACT FROM AUTHOR]

The frequency dependence of the second hyperpolarizabilities (γ ) of Kr and Xe have been measured in the visible by means of gas phase electric-field-induced second-harmonic generation (ESHG). A simple model relating the dispersion of the nonresonant electronic contribution to γ for different third-order nonlinear optical processes is derived. This model is tested by comparing the results obtained here with those obtained by other methods. [ABSTRACT FROM AUTHOR]

The nonlinear susceptibility of acetonitrile has been measured in both the gas and liquid phases by dc electric field-induced second harmonic generation (dc-SHG or EFISH). The EFISH signal for this molecule is dominated by the first hyperpolarizability β. It is shown that local field factors do not adequately describe the effect of the solvent environment. Thus it is not possible to extract ‘‘gas phase’’ values of hyperpolarizabilities from measurements made in solution. First and second hyperpolarizabilities, β and γ, have been calculated for acetonitrile using ab initio techniques. These calculations are compared to the gas phase experimental measurements. Excellent agreement is obtained when electron correlation effects are included. [ABSTRACT FROM AUTHOR]