In—Cavity Laser Raman Spectroscopy of Vapors at Elevated Temperatures. As4 and As4O6

The 632.8-nm radiation inside the cavity of an He–Ne laser is used to excite vibrational Raman spectra of As4 vapor at ∼ 610°C and As4O6 vapor at ∼ 440°C. As4 peaks are observed and assigned as follows: v1(a1), 344 cm−1; v2(e), 210 cm−1; and v3(f2), 255 cm−1. As4O6 vapor peaks are seen at 185, 253, 381, 409, 496, and 555 cm−1. An outside-cavity room-temperature spectrum of powdered As4O6 shows bands at 85, 189, 269, 371, 470, 560, and 782 cm−1. At a sample temperature of −178°C, the 85-cm−1 peak shifts to higher frequency by 4.4 cm−1. The molecular f2 fundamentals of As4O6 vapor are reassigned at 253, 346, 496, and 782 cm−1 based upon the disappearance of the 85-cm−1 low-frequency band upon going from solid to vapor, the temperature dependence of the 85-cm−1 band of the solid, comparison with assignments for P4O6, and comparison of computed absolute entropies of As4O6 vapor with entropies obtained from vapor pressure measurements, as well as literature single-crystal polarization measurements and infrared absorptions.