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Vibrational Bands of the 2-Butyn-1-yl Radical.

The 2-butyn-1-yl radical is an isomer of C4H5 and is structurally similar to the propargyl radical, which is the simplest resonance-stabilized hydrocarbon radical. The C4H5 radical is likely to be important to astrochemistry and combustion, similar to propargyl, yet little research has been done on its spectroscopic properties. In this work, seven vibrational bands of the 2-butyn-1-yl radical are reported. The radical was formed by pyrolysis of 1-bromo-2-butyne at 800 K and isolated in a low-temperature argon matrix. The experimentally observed frequencies and intensities of the seven vibrational bands were found to be consistent with QCISD predictions from the literature and with new B3LYP calculations from this work.