Knowledge Bank

A consistently good yield of the $HC2$ free radical has been obtained when an $Ar:C2H2$ mixture is codeposited at 12-14 K with a beam of argon atoms excited in a microwave discharge. Using these conditions and the DA3.002 interferometer operated at $0.2cm-1$ resolution, the $A\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}\Pi -X\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}\Sigma +$ band system of $HC2\mathrm{<mrow\; data-mjx-texclass="ORD">1,2</mrow>}$ has been observed in absorption between 3800 and $7500cm-1$. Detailed observations of the carbon-13 and deuterium-substituted species of $HC2$, which have yielded information on the position of the band origin and on the vibrational energy levels of both the ground and the excited electronic state, will be considered.