Structure and predissociation dynamics of (HCCCN)2: A high resolution infrared study

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Abstract
The IR spectrum of the HCCCN dimer has been studied using the optothermal technique. Both the ν1 and ν2 fundamentals have been recorded. Several hot bands pertaining to these two bands were also observed. The ν1 band and the ν1+ν17−ν17 hot band have been analyzed to yield accurate molecular constants for both the upper and the lower states. The structure of the HCCCN dimer is determined to be linear. The redshift of the ν1 dimer band (outside C–H stretch) from the corresponding monomer band is 2.95 cm−1, while the red shift of the inside C–H stretching fundamental band ν2 is about 67 cm−1. The predissociation lifetime of the ν1=1 state is in the range from 90 μs to 16 ns, while the predissociation lifetime of the ν2=1 state is about 450 ps. All observed hot bands which involve the ν2 vibration show narrower line widths than the fundamental ν2 band. An explanation of this phenomenon is offered which involves the angular dependence of the dynamical coupling between the inside C–H stretching and the predissociation coordinate.