Infra-red Absorption Spectrum of Heavy Phosphine. (PD₃)

Abstract

THE infra-red absorption spectrum of PD₃ has been investigated with the view of testing the applicability of the valence force field in correlating the fundamental vibration frequencies of a pyramidal molecule of the type YX₃. If it is assumed that the valence force field applies to PH₃, then one can deduce the values of the force constants of this molecule from its known vibration frequencies. This has been done by Howard¹, who gives 3.09 × 10⁵ dynes/cm, for the force required to alter the PH distance, and 0.34 × 10⁵ dynes/cm, for that required to alter the HPH angle. From these data one may compute the frequencies of the PD₃ molecule (since it is permissible to assume that these force constants are not appreciably altered by the substitution of a deuterium for a hydrogen atom). The frequencies of PD₃ are thus predicted as ₁ = 1,630 cm.¹, ₂ = 1,639 cm.¹, ₃ = 775 cm.¹, and ₄ = 871 cm.¹, all of which should be observable in the infra-red.