Spectroscopy and photophysics of the {sup 1}{Delta}{sub u} {l_arrow} {sup 1}{Sigma}{sub g}{sup +} transition of jet-cooled C{sub 4}H{sub 2}, C{sub 4}HD, and C{sub 4}D{sub 2}

Spectroscopy and photophysics of the {sup 1}{Delta}{sub u}{l_arrow}{sup 1}{Sigma}{sub g}{sup +} transition of jet-cooled C{sub 4}H{sub 2}, C{sub 4}HD, and C{sub 4}D{sub 2} reveal several vibronic transitions that can`t be completely analyzed due to the complexity of the upper state spectroscopy due to Renner-Teller and Herzberg-Teller coupling. The absence of 2{sup n}{sub 0} transitions are due to linear or quasi-linear upper state geometry. Decreasing widths of transitions occur when deuteration increases, indicating that H-atom motion plays an important role in the coupling. Suggestions are made in this paper for the dramatic observed differences in width from one vibronic level to the next. 24 refs., 10 figs., 2 tabs.