High-Resolution Study of the Difference Band ν17 − ν20 of Benzene

✍ Scribed by J. Pliva; J.W.C. Johns; Z. Lu

• Publisher: Elsevier Science
• Year: 1993
• Tongue: English
• Weight: 284 KB
• Volume: 161
• Category: Article
• ISSN: 0022-2852
• DOI: 10.1006/jmsp.1993.1232

✦ Synopsis

The difference band (\nu_{17}-\nu_{20}) of benzene centered at (779.643 \mathrm{~cm}^{-1}) has been recorded on a high-resolution Fourier transform spectrometer with the aim of obtaining accurate information about the infrared- and Raman-inactive fundamental (E_{2 u}) mode (\nu_{20}). Over 3000 lines of the band have been measured with an effective resolution of (\sim 0.0012 \mathrm{~cm}^{-1}) and assigned to 70 subbands of the two components. (\nu_{17}^{-}-\nu_{20}^{-})and (\nu_{17}^{+}-\nu_{20}^{+}), of this parallel (E_{28}-E_{2 \mathrm{u}}) transition. Neither of the two states involved in the transition is perturbed by other vibrational states, but the levels of both (\nu_{17}) and (\nu_{20}) are affected by rather strong rotational (l)-type resonance and doubling. This effect has been explicitly taken into account in the analysis of the band. In adjusting the spectroscopic constants of the two states, the origin of the upper state (\nu_{1}), and its constants (\Delta C) and (C \zeta) were held at values obtained by Hollinger and Welsh from an analysis of a gas-phase Raman spectrum since they cannot be independently determined from a difference band. To break the correlations of the rotational constants (\Delta B, q, \eta_{\jmath}), and (\Delta D), between the two states, these parameters were also adjusted independently from the upper state combination differences (R(J, K)-P(J, K)) for (\nu_{17}) and from the lower state combination differences (R(J-1, K)-P(J+1, K)) for (\nu_{20}). The spectroscopic constants obtained for the two states reproduce the observed line positions with an overall standard deviation of (0.00022 \mathrm{~cm}^{-1}). o 1993 Academic Press, Inc.