The infrared diode laser spectroscopy of the ν2+ν5-ν2 hot band of acetylene

The infrared diode laser spectrum of the nu(2) + nu(5) - nu(2) hot band of acetylene has been observed within the discharge plasma of acetylene diluted in He. The concentration of acetylene in the nu(2) state was modulated by applying a few kHz of as current, and the spectrum of the hot band was recorded selectively by the discharge modulation technique, In total, 46 P, R, and Q-branch lines have been assigned to the nu(2) + nu(5) - nu(2) hot band and molecular constants including the band origin 727.59318(27) cm(-1) were derived. The lifetime of acetylene in the nu(2) state was measured to be about 1 ms: proving that the nu(2) state is metastable. The collisional relaxation rate constant of acetylene in the nu(2) state by helium was measured to be k = 8.01 +/- 0.19 x 10(-14) cm(3) molec(-1) s(-1). (C) 1998 Academic Press.