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MO: Molekülphysik

MO 12: Posters Friday: Spectroscopy

MO 12.25: Poster

Freitag, 6. April 2001, 12:30–15:00, AT3

Determination of Line Broadening Parameters for Some Spectral Lines of Formaldehyde in the Near UV — •M. Schulz and D. Zimmermann — Institut für Atomare und Analytische Physik, TU Berlin, Hardenbergstraße 36, 10623 Berlin

We report on an investigation of pressure-induced effects on absorption lines of the vibronic bands 2₀¹4₀¹ and 2₀²4₀¹ in the A ¹A₂ − X ¹A₁ electronic transition of formaldehyde (H₂CO) between 29580 cm⁻¹ and 30700 cm⁻¹. The UV light was generated by frequency doubling of the radiation of a CR699-22 ring dye laser running with DCM Spezial in an external ring cavity allowing a continous tuning of 2 cm⁻¹. BBO and LIO crystals were used as nonlinear media yielding typically 6 mW of UV power from 250 mW input power. Absorption lengths up to 84 m were achieved in a Herriot type absorption cell. The observed line broadening coefficients decrease with increasing rotational quantum number J. For air as a perturber we obtain, e.g., 0.20 cm⁻¹/bar for J=6 and 0.15 cm⁻¹/bar for J=15. The line shift is positive in helium, nearly vanishing in neon and negative in argon, krypton, xenon, nitrogen and oxygen. For practical use we measured the detection limit of formaldehyde in air of atmospheric pressure to be about 5 ppm. This limit may be lowered considerably by using Lock-in-techniques. This work was supported by the DFG (Zi 186/6).