The Raman Spectrum of Arsenic Trifluoride and the Molecular Constants of AsF3, AsCl3 and PCl3

The Raman spectrum of AsF3 was found to consist of four lines with the frequencies ω1(1), 707; ω2(1), 341; ω3(2), 644; and ω4(2), 274 cm—1. The selection rules require a pyramidal molecule. Electron diffraction data for AsF3, AsCl3 and PCl3 are used to establish the bond angles. The entropies of the three trihalides were calculated, and the standard free energies of formation of AsCl3(l) and AsCl3(g) were determined to be —65,190 cal. and —62,718 cal., respectively, at 25°.