Context <p>The application of Raman spectroscopy for detecting furfural dissolved in transformer oil represents a highly promising approach for online monitoring for assessing the aging process of transformer insulating paper. Combining density functional theory (DFT) computational simulations with experimental measurements, the characteristic Raman spectra of the furfural molecule were analyzed, and the assignments of its key vibrational modes were determined. Furfural molecular clusters of varying sizes were constructed to investigate the effect of intermolecular hydrogen bonding forces on the Raman signals. The Raman spectra of furfural in solvents with different dielectric constants were measured. Comparison with simulation results indicates that enhanced solvent polarity induces a rearrangement of the electron cloud around the C=O bond, an increase in dipole moment, and a narrowing of the band gap. These changes thereby result in a red shift of the Raman peak position and an enhancement of scattering intensity. This work deepens the understanding, at the microscopic level, of the aggregation behavior of furfural in transformer oil and the influence of the solvent environment on its Raman characteristics.</p> Methods <p>All quantum chemical calculations were conducted using the Gaussian 16W program, and molecular structures were built using GaussView 6.0. The ground-state geometry of furfural was optimized using DFT with the B3LYP functional. The solvent effect caused by solvents with different dielectric constants was simulated and calculated using the polarized continuum model (PCM) of furfural. For all computations, the 6-311+G (2d, p) basis set was employed for C, H, and O atoms.</p>