気相サリチル酸単量体、二量体のS₀,S₁状態におけるＯＨ伸縮振動を、赤外−紫外、紫外−赤外二重共鳴分光により観測した。密度汎関数法計算との対応により、単量体における回転異性体の帰属と二量体の構造決定を行った。電子励起状態におけるケト・エノール互変異性化（分子内プロトン移動）反応について、ＯＨ伸縮振動の観測に基づき考察を行う。

The OH stretching vibrations of the monomer and dimer of jet-cooled salicylic acid were observed in the S₀ and S₁ states by using the IR-UV and UV-IR double resonance spectroscopy, respectively. With help of density functional theoretical calculations, rotational isomers of the monomer were assigined, and the structure of the dimer was determined. Excited state intramolecular proton transfer (keto-enol isomerization) is discussed based on the observation of the OH stretching vibrations.