| Abstract | Vibrational states of trans-acrolein (propenal) between 1250 and 1650 cm⁻¹ are analyzed using high-resolution (≈0.001 cm⁻¹) infrared absorption spectra. There are four fundamentals in this range, all of which have A′ symmetry: ν₉, ν₈, ν₇, and ν₆. Six additional states are directly observed via hot or combination bands: ν₁₀ + ν₁₈, ν₉ + ν₁₈, ν₈ + ν₁₈, ν₇ + ν₁₈, ν₁₆ + ν₁₇, and ν₁₅ + ν₁₇. These ten vibrational states are analyzed in two large multi-state fits, along with 25 additional states which are not directly observed but which affect the observed states by means of many perturbations. The fits involve a total of 239 adjustable variables and account for 6030 (out of 6108) assigned lines with an average error of <0.0004 cm⁻¹. But there are about 53 further vibrational states in the region of interest which are not included here. Due to this high density of states, the multi-state fits are incomplete, as well as cumbersome and not unique. Therefore individual fits for each of the four fundamentals are also described, but even with many perturbed transitions omitted they fit much less well. |
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