Cubic hyperpolarizabilities and local electric field in alkanes and substituted alkanes

Abstract

Cubic hyperpolarizability of a family of alkanes and substituted alkanes with a general formula CH3–(CH2)n−2CH2X (6 ≤ n ≤ 16 and X = H, Cl, Br, I) was measured by using third-harmonic generation at 1.064 μm. Using an additivity model and Onsager’s formulas for local-field factors, the cubic hyperpolarizabilities of the and –CH2X groups were determined, and the following values were obtained (in 10−37 esu): γCH2 = 6.6, γCH2X = 5.2 (X = H), 9.3 (X = Cl), 18.3 (X = Br), and 41.4 (X = I). For C–X bonds the corresponding values are γC–H = 2, γC–C = 1.2, γC–C = 7.7, γC–Br = 13.6, and γC–H = 30.6. A comparison of the above values with those found for other organic solvents shows the importance of molecular geometry in the additivity model.