Spectroscopic properties and anharmonic force field of furan (C4H4O) and methylfuran (C5H6O): A DFT study

Furan demonstrates high calorific values and is of great significance in combustion and atmospheric chemistry. This study establishes a benchmark database for spectroscopic constants and anharmonic force fields of furan and methylfurans by integrating vibrational second-order perturbation theory (VPT2) with density functional theory (DFT). Benchmarking analysis reveals the B3LYP/cc-pVQZ level delivers spectroscopic predictions exhibiting small deviation from experimental datasets, and key parameters including rotational constants (A₀/B₀/C₀ within 0.3 %), fundamental frequencies (ν_i within 3 %), etc. This level provides anharmonic IR spectra and enables predictions of anharmonic constants, cubic/quartic force parameters, establishing critical references for guiding high-resolution rovibrational spectroscopy of furan derivatives.