Applications of Multiphoton Absorption to Atomic and Molecular Spectroscopy

2 Applications of Multiphoton Absorption to Atomic and Molecular Spectroscopy 

The first two-photon absorption in the molecular gas phase was observed in benzene by HOCHSTRASSER et al. [8.96]. An extensive two-photon excitation spectrum of the transition in benzene including the hot bands 

The rotational selection rules, which are AJ = 0, 1 for single-photon transitions, are aJ = 0, 1, 2 for two-photon transitions, where the value of aJ depends on the polarization of the incident radiation (see Fig.8.41). 

While for tziX9-photon transitions the parity of the excited state is the same as that of the absorbing ground state, three-photon transitions excite states with the same parity as single-photon transitions. 

Both methods therefore complement each other in high-resolution laser spectroscopy in the vacuum ultraviolet region, where single-photon spectroscopy is impeded by lack of tunable lasers. With intense light of a pulsed 

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