Two-Photon Spectroscopy in the Gas Phase
In the methods of molecular spectroscopy, molecular information of high precision can be obtained by high resolution measurements in the gas phase. Here one-photon absorption in the ultraviolet has yielded important information. Whereas one-photon absorption selects g→u parity transitions, two-photon processes select g→g transitions. Selection rules also differ in many other ways. As a consequence two-photon spectroscopy opens up the possibility of observing many new transitions in molecular spectroscopy, particularly if they are carried out in the gas phase. We here demonstrate, employing the classic example of benzene, how new transitions are uncovered and a two-photon molecular spectrum in the gas phase assigned using this new technique. It is also shown that the intensity of the laser system suffices to prepare quantum states by two-photon absorption in the collisionless gas phase. This opens up a plethora of new experimental possibilities. Lifetimes are here given as an example.
KeywordsMolecular Spectroscopy Vibronic State High Resolution Measurement Ground State Frequency Prepare Quantum State
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