Becher-Weg 27, D-55128 Mainz, Germany Fraunhofer Institute Applied Solid State Physics (IAF), Tullastraße 72,
D-79108 Freiburg, Germany We present comparative measurements of carbon monoxide by a quantum cascade as well as a lead chalcogenide laser in a two-laser spectrometer designed for trace gas measurements in the atmosphere. Both lasers measure the P(25) line of CO at 2037.025 cm-1. At 298 K, this line has a strength of 5.13 10-21 cm molecule-1, which is about a factor of 100 smaller compared to the strongest lines in the fundamental CO absorption band. However, this allows a discussion of the small signal behavior of the lasers within the spectrometer in combination with the simple handling of diluted CO gas samples. Calibration gas as well as ambient air measurements are presented and discussed with respect to noise and signal stability. Sensitivity improvements of sub-ppbv trace gas detection through the use of quantum cascade lasers will be discussed.
B9.
Rotationally resolved infrared spectrum of the charge transfer complex [Ar-N2]+ H. Linnartz1,2, D. Verdes1 and J.P. Maier1
1Department of Chemistry, Klingelbergstrasse 80, CH 4056 Basel
2Fysische Chemie, Vrije Universiteit Amsterdam, De Boelelaan 1083,
NL 1081 HV Amsterdam Difficulties in preparing cluster ions for spectroscopic studies have limited our understanding of intermolecular forces in charged complexes that are typical of many reactive intermediates. In this contribution the infrared spectrum of the charge transfer complex [Ar-N2]+, recorded in a supersonic planar plasma with a tunable diode laser spectrometer, is presented. More than 70 adjacent rovibrtional transitions were measured near 2272 cm-1 and assigned to the molecular nitrogen stretching fundamental in the 2+ ground state. An example is given in the figure. The accurate structural parameters that are determined confirm a linear structure and show that the major part of the charge is located at the argon atom. The latter result is surprising and implies a charge switch of the cationic center upon complexation.
A plasma modulated TDL spectrum of the charge transfer complex [Ar-N2]+. More information is available from Science 297 (2002) 1166.
