Transient laser frequency modulation spectroscopy

Explicitly time-dependent implementations of optical frequency modulation spectroscopy have been recently applied to a wide range of problems in chemical physics. We provide a brief description of the methodology, with an emphasis on its intrinsic advantages for interrogating transient species. Several examples highlight the application of the technique to high-resolution absorption spectra of free radicals, rate measurements for gas-phase reactions, and Doppler spectroscopy of the gas-phase products of photoinitiated reactions.