FTIR study of D and 13C substituted C2H in solid argon

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Abstract
An extensive FTIR isotopic matrix study using deuterium and carbon-13 has been conducted on the midinfrared spectrum at 250 to 4800 cm−1 of the C2H ethynyl radical produced by the vacuum UV photolysis of acetylene. An absorption at 2104 cm−1 can be assigned to a combination band involving one quantum each of the ν2, bending and the ν3, C–C stretching vibrations. This result implies an unexpectedly low value of ∼260 cm−1 for ν2. Identification of the combination band in this work gives the first indication of the value of the ν2 fundamental, which has not otherwise been observed. The results of carbon-13 substitution on a band at 3610 cm−1 do not appear to be consistent with its previous assignment to the ν1, C–H stretching vibration of C2H. However, carbon-13 shifts for the C2D band at 2798 cm−1 support its assignment to ν1. Absorptions corresponding to several vibronic bands of the A 2Π←X 2Σ+ transition, which have recently been reported in gas phase studies using color center laser spectroscopy, are observed in the matrix spectra, confirming that these bands originate from the lowest vibrational level of the ground state. The effects of carbon-13 substitution on these bands are reported.