Potential Energy Curves from Electronic Band Spectra

Then the J values at which these branches turn around are 

Only onepf these values is physical (positive). Since the upper electronic state is commonly more weakly bound than the lower state Rg / ), one usually observes B B —in which case the R branch is the one that turns around Jt 0). Both the P and R branches then run to lower frequencies for large J (since (B — B ) 0), and the band is said to be shaded to the red. When R kR , the band is shaded to the blue. The rotational fine structure is barely resolved in the Na2 fluorescence excitation spectrum of Fig. 4.3, but the asymmetric shading of the vibrational bands to the red is clearly asserted. It occurs because the equilibrium separation of Na2 is considerably larger in the than in the 

7 POTENTIAL ENERGY CURVES FROM ELECTRONIC BAND SPECTRA 

The spectroscopic techniques described in this and the preceding chapters yield an impressive array of molecular constants, in terms of which the rovibrational energy levels may be expanded to desired accuracy via 

For example, spectral lines in vibration-rotation spectra of heteronuclear diatomics are readily assigned to particular v J ) v J ) transitions by inspection. Their positions may be analyzed using Eqs. 3.64,3.65, 3.68, and 3.81 to extract the ground-state constants o , B , D , a , — In homonu- 

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