Knowledge Bank

Triplet HC$\mathrm{<mrow\; data-mjx-texclass="ORD">5</mrow>}$H, along with several derivatives (RC$\mathrm{<mrow\; data-mjx-texclass="ORD">5</mrow>}$R$\prime$; R, R$\prime$ = H-, CH$\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}$-, (CH$\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}$)$\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}$C-), have been observed and characterized by IR, UV-vis, and ESR spectroscopy in cryogenic matrices. The structural similarity of RC$\mathrm{<mrow\; data-mjx-texclass="ORD">5</mrow>}$R molecules to known interstellar molecules allows their consideration as plausible interstellar species. The electronic spectrum of HC$\mathrm{<mrow\; data-mjx-texclass="ORD">5</mrow>}$H clarifies some ambiguities concerning earlier attempts to detect this species and provides a foundation for further gas-phase spectroscopic studies. The optical spectra of HC$\mathrm{<mrow\; data-mjx-texclass="ORD">5</mrow>}$H and analogs also exhibit rich vibronic fine structure, and will be discussed in the context of the diffuse interstellar bands (DIBs). In addition, the photoisomerizations of RC$\mathrm{<mrow\; data-mjx-texclass="ORD">5</mrow>}$R molecules will be briefly discussed. N. P. Bowling, R. J. Halter, J. A. Hodges, R. A. Seburg, P. S. Thomas, C. S. Simmons, J. F. Stanton, and R. J. McMahon. J. Am. Chem. Soc. (2006) ASAP.