UV SPECTROSCOPY OF RADICALS PRODUCED IN THE PHOTYLYSIS OF DIACETYLENE AND ACETYLENE IN INERT MATRICES,
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Date
1981
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Ohio State University
Abstract
A Series of experiments has been carried out in the 1200-4000 A region to characterize the molecular species formed on the photodissociation of $C_{4}H_{2}$ and $C_{2}H_{2}$ trapped in argon at 12 K. Band systems at 60266 and $71633 cm^{-1}$ which appear both in photolyzed $C_{2}H_{2}$: Ar and unphotolyzed $C_{4}H_{2}$ samples are identified as the nR-X (n = 3,4) Rydberg series of $C_{4}H_{2}$. The $\sigma g^{+}$, C $\equiv C$ stretching and $\Pi_{g}$, C-H bending modes observed at $v_{2} ~205b cm^{-1}$ and $v_{6}{550} cm^{-1}$ for the 3R-X transition are shifted to 2000 and $400 cm^{-1}$ respectively, on deuteration of the acetylene parent. The 4R-X transition exhibits a progression in the $C\equiv C$ stretching mode, $v_{2}\sim2190\sim \mbox{cm}^{-1}$. A band system at 1945 A appearing weakly in photolyzed $C_{2}H_{2}$ and strongly in photolyzed $C_{4}H_{2}$ samples may be tentatively assigned to a new transition from the $X^{2}\Sigma$ of the $C_{4}H$, butadinyl radical. The C-H bending vibration $v^{\prime}_{5}~620 \mbox{cm}^{-1}$, and the $C\equiv$ C stretching vibration $v^{\prime}_{2} or v^{\prime}_{3}~2150 \mbox{cm}^{-1}$ are Shifted to 480 and $2080 cm^{-1}$ respectively, on deuteration of the parent $C_{2}H_{2}$ and $C_{4}H_{2}$. Evidence for transitions of the $C_{2} H$ ethynyl radical and linear $C_{n}$ molecules will also be discussed.
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