Raman Effect of Acetylenes II. Diiodoacetylene, Liquid Acetylene and Deuteroacetylenes

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Abstract
An apparatus consisting of eight discharge tubes for Raman work has been designed which is more convenient than the usual helical design of these light sources. It is possible to arrange these eight tubes concentrically around a Raman tube of any diameter. Cylindrical filters of any dimensions can be interposed with great convenience. The vibration Raman spectra of C2I2: 191.3, 310.2, 627.0 688.2 and 2109.4; liquid C2H2: 381.6, 618, 631, 1762, 1959 and 3338; gaseous C2H2: 1973.8 and 3373.7; gaseous C2HD: 1851.2 and 3334.8; gaseous C2D2: 1762.4 and 2700.5 cm—1 have been observed and are interpreted in the usual manner on the basis of symmetry considerations. Striking differences in the spectra of liquid and gaseous acetylene (C2H2) indicate a serious distortion of the molecules in the liquid state. The extent of this disturbance seems to change completely the symmetry of the molecules of the liquid which are no longer linear as in the gaseous state. Certain Raman lines are accompanied by faint satellites which fit a rotation formula and may be due to rotation effects. The free energies of C2HD and C2D2 were calculated and the free energy change of the reaction C2H2+C2D2⇆2C2HD has been evaluated and the equilibrium constant determined for a series of temperatures.

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