15min:

H. VALIPOUR AND D. ZIMMERMANN, Fachbereich Physik, Technische Universität Berlin, Germany.

Line shift and line broadening coefficients and \gamma have been measured for 21 rotational lines of the P and R branch of the ₁+3₃ band of acetylene at 789 nm using a tunable cw semiconductor laserdiode system. The absorption cell was of the multi-pass Herriot-type with an effective absorption length of 35 m. Up to now, self-broadening and broadening by N₂, Ar and air perturbers have been investigated. Taking air-broadening as an example we obtained \gamma = 0.176(12) cm^-1/bar and = 0.012(2) cm^-1/bar for the P(4) line. With increasing value of J the values of \gamma decrease, e.g. to 0.147(2) cm^-1/bar for R(13) whereas increases to 0.016(2) cm^-1/bar. A similar behaviour has been observed for the case of other foreign gas perturbers and for self-broadening. The present investigation might be of interest for the reliable detction of small amounts of acetylene in air of atmospheric pressure. In our system we could detect a minimal concentration of 1 µbar acetylene in a N₂ atmosphere of 15 mbar pressure.