Infrared and Raman spectra and theoretical calculations for benzocyclobutane in its electronic ground state

Fluorescence excitation and ultraviolet absorption spectra and theoretical calculations for benzocyclobutane: Vibrations and structure of its excited S1(π,π*) electronic state

“…The near coincidence of these frequencies was demonstrated by observation of their infrared and Raman band types. 8 From the UV spectrum in our present study we find that the overtone levels of these vibrations are in Fermi resonance and occur at 411 and 417 cm −1 with mixed 2ν 22 and 2ν 42 character. Aside from the Fermi interaction, as can be seen in Figure 6, both ν 22 and ν 42 , as well as two other relatively low frequency vibrations ν 41 (B 2 ), the benzene ring out-of-plane bending, and ν 21 (A 2 ), the benzene ring twisting, are all nearly harmonic.…”

“…As discussed in Ref. 8, the structure for the ground state is quite typical for what is expected for a bicyclic molecule containing the benzene ring. Namely, the carbon-carbon bond distances are all 1.39 ± 0.01 Å for BCB as well as for IND and TET.…”

“…Figure 3 shows the structures for both IND and TET with selected bond distances and angles from the MP2/cc-pVTZ calculations performed on the ground state. 8 Selected bond distances and angles of IND 1 and TET 2 in their S 1 (π ,π * ), electronic excited state are also shown. The calculations performed for IND in the excited state 1 utilized the CIS/6-31G(d) basis set, whereas the basis set used for the excited state calculations for TET 2 was CIS/6-311++G(d,p).…”

“…21 The geometrical parameters calculated in the present work for the BCB electronic ground state using the CASSCF method were very similar to the previous MP2/cc-pVTZ results. 8 In the previous work B3LYP/cc-pVTZ calculations were utilized to compute the vibrational spectra and these were compared to the experimental vapor and liquid phase infrared and Raman spectra. Frequencies for the ground state below 1450 cm −1 were scaled with a factor of 0.985, frequencies in the 1450-2000 cm −1 region were scaled by a factor of 0.973, and frequencies above 2000 cm −1 by 0.961 based on previous work.…”

Vapor-phase infrared and Raman spectra and ab-initio calculations of the axial and equatorial forms of cyclohexane-d1 and d11

“…The density functional theory (DFT) B3LYP method [11,12] was used with the cc-pVTZ basis set. The scaling factor of 0.961 was used for the vibrations of interest, based on previous work [13][14][15][16][17][18], which also has shown us that B3LYP/cc-pVTZ calculations do a better job than MP2/cc-pVTZ for reproducing vibrational frequencies.…”