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The proof of quantum theory lies mainly in the data of spectroscopy. Individually the peaks of a molecule’s spectrum represent emission or absorption transitions between energy levels, and collectively they build a richly detailed picture of the manifold of energy levels accessible to the molecule while it is engaged in one or more of its modes of motion. The effect of a photon absorbed by a molecule from a spectrometer beam depends on the energy of the photon. Microwave photons excite rotational transitions, infrared photons rotational and vibrational transitions, and visible or ultraviolet photons rotational, vibrational, and electronic transitions. Photons from a radio frequency source excite spin transitions in an applied magnetic field. Rotational spectra are illustrated in Sec. 5.1 (the program Ro3), rotational-vibrational spectra in Sec. 5.2 (programs Peaks, Rovi2, Symtop1, and Symtop2), vibrational-electronic spectra in Sec. 5.3 (the program Viel2), and rotational-vibrational-electronic spectra in Sec. 5.4 (the program Roviel). Spin resonance spectra are illustrated in Sec. 5.5 (programs 2dnmr, Nmr, and Esr). The chapter closes with an account of Fourier-transform techniques for analyzing spectrometer data (programs Irft and Nmrft).
KeywordsNuclear Magnetic Resonance Electron Spin Resonance Electron Spin Resonance Spectrum Diatomic Molecule Coupling Interaction
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