Photodissociation of NaBr, Nal, and KI vapors and collisional quenching of Na* (3 2P), K* (4 2P), and K* (5 2P) by foreign gases

Abstract

Fluorescence from excited alkali atoms (A*) may be produced by photodissociation of alkali halide (AX) vapor. Fluorescence efficiencies have been determined as a function of the photodissociation wavelength, λ0, for Na* (3 2P) from NaBr and for K* (4 2P) and K* (5 2P) from KI. Employing the Stern-Volmer relation, cross sections, Qq, for the collisional quenching of the A* electronic excitation may be determined from the attenuation of the A* fluorescence that is observed upon introduction of a foreign gas. Because A* may be produced with different average speeds by varying λ0, this method permits the determination of the dependence of Qq on relative collision speed, g. Employing this method, Qq was determined to decrease monotonically with increasing g for Na* (3 2P)+Br2 (AX = NaBr) and K* (4 2P)+C2H4, CF3Cl, and SO2 (AX = KI). Moreover, values of Qq were determined at a particular g value for K* (4 2P)+I2 and K* (5 2P)+I2, HCl, and DCl. Alternatively, premixing the quenching gas in a large (∼ 100-fold) excess of Ar thermal moderator (Ar failed to quench any of these A* levels) makes possible the measurement of Qq for a thermal distribution in g. Thermal results (800–900°K) obtained by this method are reported for the quenching of Na* (3 2P) (AX=NaI), K* (4 2P), and/or K* (5 2P) by N2, CF3Cl, H2, H2O, CH3OH, CF4, CH4, C2H6, C2H4, and SO2. In general, for any particular quenching gas, Qq[K* (5 2P)] > Qq[Na* (3 2P)] ≳ Qq[K* (4 2P)]. The difference between K* (52P) and K* (4 2P) [or Na* (3 2P)] is sometimes quite large; for CH4, for example, Qq[K* (5 2P)]/Qq[K* (4 2P)] > 60. For I2, however, the trend is dramatically reversed with Qq[K* (5 2P)]/Qq[K* (4 2P)]=0.2. Effects of isotopic substitution were also examined; no difference in Qq was measured for H2 vs D2, H2O vs D2O, C2H4 vs C2D4, or HCl vs DCl. However, for K* (5 2P), Qq(CH4)/Qq(CD4) ≈ Qq(C2H6)/Qq(C2D6) ≈ √2. All of these results are discussed in terms of the likely forces between the reactants and the possibility of a change-transfer intermediate.

Inverse Theorems on Generalized Padé Approximants

“…A comparison of our cross sections with the other values listed in table 1 is not very useful because the experimental conditions, especially the temperatures of the potassium vapour (shown with the references), are quite different. There is reasonable agreement between our results and those of Earl and Herm (1974) for H2 and N2, but the CH4 cross sections differ by a factor of two. The lack of consistency between our results and those determined by Hooymayers and Lijnse (1969) is attributed to the difficulties inherent in the flame spectroscopy method.…”

“…Although far fewer studies of the more highly excited states have been reported, quenching of the 52P state in potassium has been investigated by flame spectroscopy (Hooymayers and Lijnse 1969), by Stern-Volmer quenching of atomic fluorescence (Earl and Herm 1974), and by following the decay of the fluorescence after photodissociation of KI (Lin et a2 1984). In the present investigation, potassium atoms in the presence of a buffer gas were excited by pulsed dye-laser radiation to one of the 5*P fine structure (FS) states, and the time evolution of the resulting fluorescence was registered using a monochromator, photomultiplier and transient digitiser.…”

Reaction pathway, energy barrier, and rotational state distribution for Li (2 2PJ)+H2→LiH (X 1Σ+)+H

“…34 The obtained electronic quenching efficiencies of Li (2 2 P J ) by H 2 are relatively larger than those reported for Na and K in their lower lying states. 33,[35][36][37][38] Whether such abnormal quenching behavior will be reflected in the chemical reaction is an interesting issue not yet known. Therefore, in this work we seek to find the reaction mechanism for the Li (2 2 P J ) with a H 2 reaction.…”

Spin-orbit relaxation and quenching of cesium 72Pin mixtures of helium, methane, and ethane

“…Generally, the J = 3/2 level exhibits a rate that is faster than that of the J = 1/2 component by a factor of up to 4.5 [26]. However, the J = 1/2 state is more rapidly quenched in mixtures of Cs(6 2 P 1/2 ) + (H 2 , HD, or CH 4 ) [27], and equally quenched in mixtures of K(4 2 P 1/2 ) + C 2 H 4 [28]. The current results of Table II indicate ratios of σ 20 /σ 10 of 4.1, 1.8, and 1.9 for helium, methane, and ethane, respectively.…”