Basis sets Raman band intensities

The IR spectra of tetrazines are found to be as expected for this system literature leading to data on simple derivatives is found in <84CHEC-I(3)531>. Some more recent literature can be found for the diode laser spectrum and analysis of the 882 cm band of -tetrazine <84JSP(107)373>, the diode laser spectrum and analysis of the 1103 cm band of -tetrazine <85JSP(l 12)340>, and the comparative study by Wiberg of azines—the effect of basis set on the calculated vibrational frequences, infrared, and Raman intensities <90JST(244)6i>. 

From Table 3.5 we also observe that it is possible to calculate the intensities of infrared and Raman bands, but in order for this process to generate accurate results we need to employ large, diffuse basis sets. This is because computation of dipole moments and polarizability derivatives require that the tail of the electron density region be properly modeled. Specialized basis sets have been developed for this purpose, and a comparison of their performance can be found in [20]. 

High level HF/SCF calculations on ethylene using analytic derivative methods have been reported by Frisch et al. [341]. Their results are presented in Table 10.4. Vibrational frequencies and infrared intensities are also given. Interestingly, even at this high level of SCF theory the frequencies for vio(B]u) and vi](B2g) are predicted with reversed order. There are, however, no difficulties in assigning these bands for the correct normal mode on the basis of symmetry properties of die respective normal modes and the fact that B2g mode is Raman active wdiile Biu -infrared active. Both infrared and Raman intensities are relatively well predicted at the SCF large basis set calculations. 

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