Vacuum UV spectra of flash lamps down to 115 nm: N2 and Xe sparks
Shaoliang Zhang1, Cornelius Zetzsch2
1 Université de Provence
2 University of Bayreuth
2 University of Bayreuth
P.8 in Poster Session
Laser flash photolysis at fixed wavelengths at 193 and 248 nm or other fixed wavelengths has become popular for kinetic experiments. On the other hand, flash lamps for pulsed vacuum UV photolysis have been introduced by Welge and coworkers in 1967 and many authors employed them in various kinetic studies. It was convenient to use a small flow of N2 at one atmosphere in those spark lamps but the life of the electrodes was rather limited.Nowadays Xe lamps for the vacuum UV with a MgF2 window have become commercially available, and we determined the spectral distribution of both lamps by a 0.2 m vacuum UV monochromator (Minuteman 305M) with a holographic grating (1200 lines/mm, optimized for the range 100-300 nm) and a solar blind photomultiplier with CeTe photocathode (EMR Schlumberger 541 09 F). The total light path was flushed by a slow flow of high-purity N2 (99.999%) taken from a liquid-nitrogen tank. The spectral response is estimated from a spectrum of a similar D2 lamp from the manufacturer provided by the PTB (Physikalisch-Technische Bundesanstalt).
Our N2 spark lamp was similar to those described by Welge et al. (1967), employing a lowinductancecapacitor (10 nF, charged to 11 kV). The Xe flash lamp (Perkin-Elmer FX 1165) was operated at 1 kV with a capacitance of 570 nF. Both flash lamps were triggered at a constant repetition rate of 1 s-1, and the signals were recorded by integrating the output spikes from an electrometer operational amplifier (Keithley 301) using a PC-based chromatography data acquisition system (HP Chem Station and ADC 53900E).
The spectrum of the N2 lamp contains mainly the Lyman-Birge-Hopfield bands (see Huber and Herzberg, 1979, for references) over a wide range of wavelengths, and the Xe lamp emits mainly ethe transitions from the A(3Σu+) and the B (1Σu+) excited states to the X (1Σg+) state. These emissions are described in the monograph of Huber and Herzberg (1979) as "unclassified absorption bands longward and shortward of the resonance line at 68045.66 cm-1 (146.96 nm); pressure broadening of this line due to molecule formation; continuous emission 68000 - 50000 cm-1 (147.0 – 200.0 nm) with maximum near 68030, 67070 cm-1 (147.0, 149.1 nm), first continuum and about 58800 cm-1 (1670 nm, second continuum)".
These features of the Xe lamp FX 1165 are confirmed but differ markedly from schematic spectra released in one of the catalogues from the manufacturer (BRO_1100tb.pdf, see figure). The advantages and disadvantages of using such flash lamps (as compared to the 193 and 248 nm lines of ArF and KrF lasers) will be discussed at the poster; digital files of the spectra are available upon request.
References
K.H. Welge, J. Wanner, F. Stuhl, A. Heindrichs (1967) Rev. Sci. Instruments 38, 1728-1730.
K.P. Huber and G.Herzberg, Molecular Spectra and Molecular Structure. IV. Constants of Diatomic Molecules, Van Nostrand Reinhold , New York 1979.
Acknowledgements We thank Heraeus Noblelight Company, Hanau, for providing a spectrum of a D2 lamp with MgF2 window, calibrated by the PTB (Physikalisch-Technische Bundesanstalt, Braunschweig) and the DFG for funding the research project ATMOCHEM within the joint
CNR-INSU/DFG programme.