Abstract
The infrared diode laser spectrum of the ν2+ ν5− ν2hot band of acetylene has been observed within the discharge plasma of acetylene diluted in He. The concentration of acetylene in the ν2state was modulated by applying a few kHz of ac current, and the spectrum of the hot band was recorded selectively by the discharge modulation technique. In total, 46P,R, andQ-branch lines have been assigned to the ν2+ ν5− ν2hot band and molecular constants including the band origin 727.59318(27) cm−1were derived. The lifetime of acetylene in the ν2state was measured to be about 1 ms, proving that the ν2state is metastable. The collisional relaxation rate constant of acetylene in the ν2state by helium was measured to bek= 8.01 ± 0.19 × 10−14cm3molec−1s−1.
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