Effect of¹⁸O on the infrared absorption intensity of the phosphorus oxychloride symmetrical vibrations

The infrared absorption of normal and 97 at. % ¹⁸O phosphorus oxychloride in the 4000-200 cm^-1 region has been investigated for cyclohexane and other solutions. The relative integrated absorption of all their symmetrical (A₁) bands was estimated by multiplying each molar index of absorbancy by the corresponding half-width. The respective normal and labeled compound F sums for the A₁ species were found to disagree by about 5%. The origin of this discrepancy, as well as the different effect of a change of solvent on the half-width and integrated area of the P=¹⁶O and P=¹⁸O stretching bands is discussed.