Optical Spectra of an Isoelectronic Series; the π←π Transition in Phenyl Isocyanide, Ethynylbenzene, and Benzonitrile

• Published in: The Journal of chemical physics 1972-01, Vol.56 (9), p.4385-4393
• Main Authors: Muirhead, Alan R., Hartford, Allen, Huang, Kwo-Tsair, Lombardi, John R.
• Format: Article
• Language: English
• ISSN: 0021-9606; 1089-7690
• DOI: 10.1063/1.1677877

In this work we study the lowest-lying singlet π*←π transition in the isoelectronic series phenyl isocyanide, ethynylbenzene, and benzonitrile. The spectrum of phenyl isocyanide is analyzed for the first time and is found to be very similar to that of ethynylbenzene. The 000 band is assigned at 2723 Å. Rotational analyses are reported on the 000 and 23501 bands in phenyl isocyanide. Changes found in rotational constants for the 000 band are Δ A = −0.00789 cm−1, Δ B = −0.00101 cm−1, and Δ C = −0.00101 cm−1. Origin of the electronic transition is set at 36 712.96 cm−1. Dipole moment changes on excitation are determined for all three molecules by the Stark effect. For benzonitrile Δμ = 0.31 D, more than twice the change in the other two molecules. The differences in the over-all spectrum and dipole moment change for benzonitrile compared to the other two molecules are explained in terms of the possible influence of intramolecular charge transfer.