1II — 1E+ transition

For a one-photon, electric dipole transition, the parity selection rule is always + <-> —. In terms of e/f symmetry, Fig. 6.1 illustrates a 1II — 1E+ transition with rotational lines Q/e, Pee, and Ree-... 

Measurements by photographic photometry require careful calibration due to the nonlinear response of photographic plates saturation effects can lead to erroneous values. Line profiles can be recorded photoelectrically, if the stability of the source intensity and the wavelength scanning mechanism are adequate. Often individual rotational lines are composed of incompletely resolved spin or hyperfine multiplet components. The contribution to the linewidth from such unresolved components can vary with J (or TV). In order to obtain the FWHM of an individual component, it is necessary to construct a model for the observed lineshape that takes into account calculated level splitttings and transition intensities. An average of the widths for two lines corresponding to predissociated levels of the same parity and J -value (for example the P and R lines of a 1II — 1E+ transition) can minimize experimental uncertainties. A theoretical Lorentzian shape is assumed here for simplicity, but in some cases, as explained in Section 7.9, interference effects with the continuum can result in asymmetric Fano-type lineshapes. 

Consider transitions between a pair of mutually interacting 1 + and 1II upper states and an unperturbed 1 + lower state. The 1E+ — 1E+ system has only one P and one R branch, and the transition amplitudes are... 

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