使用第二代步進式傅氏紅外光譜法搭配多重吸收反應槽研究時間解析的氣態不穩定分子之吸收光譜，其光譜解析度可達 0.075 cmˉ¹。利用此方法可測量許多不穩定的自由基與其異構物的紅外光譜，並瞭解其相關之化學動力學，部分光譜可以解析轉動譜線。光譜之指派係藉由將觀測到的振動波數、紅外強度及轉動譜帶輪廓與以理論計算所預測者比較。最近所觀測到的大氣化學中極重要的庫利基中間體 CH₂OO 之紅外吸收光譜，即為利用此方法的最佳例子。

We employed a second-generation step-scan FTIR coupled with a White cell to investigate IR absorption spectra of gaseous reaction intermediates with resolution up to 0.075 cmˉ¹. With this method IR spectra with partially resolved rotational structures of many unstable free radicals and their isomers have been detected; their reaction kinetics was also investigated. The assignments were made according to comparison of observed vibrational wavenumbers, IR intensities, and rotational contours with those predicted with quantum-chemical calculations. The observation of the simplest Criegee intermediate CH₂OO serves as a good example for such an application.