Abstract

A narrowband extreme ultraviolet (XUV) laser is applied in a spectroscopic study on molecular hydrogen in the wavelength domain 86-90 nm. The XUV-radiation is generated by third harmonic generation of the output of a frequency-doubled dye laser, running on Coumarine dyes in the blue-green region. Crossed laser/molecular beam techniques for sub-Doppler resolution and I XUV + I UV photionization for sensitive detection were applied in this study. Thus spectra of isolated and resolved rotational lines in the C^l∏_u-X¹Σ_g⁺, b¹σ_u⁺-x¹Σ_g⁺, D¹∏_u-X¹Σ_g⁺, and B’¹Σ_u⁺-X^lΣ_g⁺ systems could be recorded with a linewidth of 0.3 cm^–1. These spectra were recorded with XUV-light of frequency six times that of the output of the fundamental dye laser. This allows for on-line frequency calibration, in an absolute sense. Transition frequencies were determined from a simultaneously recorded I₂-absorption spectrum in the visible domain using computerized intrapolation procedures. Similarly recorded markers of an etalon were used for scan linearization. These procedures resulted in an absolute accuracy of 0.04 cm^–1 in the XUV-domain. Comparison of the presently obtained data with data from previous classical (i.e. non-laser) spectroscopic studies show an improvement in accuracy by a factor of five.

© 1996 IEEE