Radiative lifetime and quenching cross section of the B 1π u state of K2 by time correlated single photon counting using a modelocked He-Ne laser J. Chem. Phys. 66, 4509 (1977); 10.1063/1.433703Rotational lifetimes and selfquenching cross sections in the B 3 Π ou + state of 127I2 Fluorescence lifetimes, self-quenching cross sections, and foreign gas quenching cross sections have been measured for 1 2 B 3 IIO u +) by direct observation of fluorescence decay for excitation in the region 640-499.5 nm, corresponding to excited electronic state levels between v' "" 5 and v' "" 70, close to the dissociation limit. The foreign gas experiments represent the first measurement of foreign gas quenching rates using lifetime methods. A pulsed tunable nitrogen-Iaser-pumped-dye laser with a linewidth of 0.3 to 0.7 nm and a pulse time of less than 10 -8 sec was used as the excitation source. Lifetimes were found to be strongly dependent on v', varying from less than 0.4 J.l.sec to greater than 7 J.l.sec. Seif-quenching cross sections showed less v' dependence, varying between 47 and 90 X 10-16 cm 2 • Foreign gas quenching cross sections were measured for Ar, Br 2 , CO 2 , H 2 , He, Kr, N 2 , NO, Ne, °2, SF 6 , and Xe, and showed a dependence on both v' and the gas used. Values for light gases, such as H2 and He, were typically I X 10-16 cm 2 or less, while values for Xe were as high as 23 X 10-'6 cm 2 •

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A new analytic technique was developed to determine quantitatively the concentration of gas-phase species at concentrations well below the measurement capabilities of atomic absorption and mass spectroscopy. The method involves injecting an excess of an energetic metastable species, N2(A3Σ+u) in this experiment, into a gas stream containing the species to be measured, Bi in this case. Energy transfer from the metastable to the sample species results in excitation and subsequent rapid emission of light. The intensity of the light emitted at the wavelengths characteristic of the sample species is a function of, and hence a measure of, the concentration. Concentrations as low as 1.5×104/cm3 were measured. Greater sensitivity is possible with more efficient optical detection.

A simple and relatively inexpensive new technique for qualitatively and quantitatively measuring various gas-phase species in a flow and the apparatus for implementation are described. Detection of atomic species has been demonstrated from concentrations greater than 10(10) atoms/cm(3) to approximately 10(4) atoms/cm(3). Several classes of molecules can also be detected quatitatively with the method, although with somewhat reduced sensitivity. The method, metastable transfer emission spectroscopy (MTES), is particularly useful in materials analysis. Possible applications including the analysis of gas, liquid, and solid samples and the determination of vapor-pressure curves are discussed.