High resolution rotation–vibration Raman spectra of acetylene. I. The spectrum of C2H2

Abstract

The Raman spectrum of gaseous acetylene was excited in a multiple-reflection Raman cell by a single-moded Ar⁺ laser and recorded photographically; the gas pressure was 380 Torr and the spectral slit-width ~0.1 cm⁻¹. The three Raman-active fundamentals ν₁, ν₂, and ν₄¹ of C₂H₂ were analyzed to give the band origin, ν₀, and the upper state constants, B₁ and D₁; accurate infrared values of the lower state constants, B₀ and D₀, were assumed in the analysis. The values of the constants for the ν₂ band illustrate the accuracy obtained: ν₀ = 1974.317(2), B₁ = 1.170419(14), D₁ = 1.579(18) × 10⁻⁶ cm⁻¹. Five difference bands originating in transitions from the low-lying ν₄ = 1 and ν₅ = 1 vibrational states were also measured and analyzed.