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We present a kinetic study of the collisional behaviour of Ba[6 s 5 d ( 3 D  J  )], 1.151 eV above the 6 s  2 ( 1 S 0 ) ground state ( J  = 1, 1.120,  J  = 2, 1.143,  J  = 3, 1.190 eV) in the time-domain.  This optically metastable atom was generated following the pulsed dye-laser excitation of atomic barium vapour at elevated temperatures at λ = 553.5 nm {Ba[6 s 6 p ( 1 P 1 )] ← Ba[6 s  2 ( 1 S 0 )]}. Ba( 3 D  J  ) was then produced in the long-time domain following a complex series of collision and radiative processes within the energy manifold of atomic barium.  The collisional behaviour of this species in the presence of neon and argon, and ground state Ba[6 s  2 ( 1 S 0 )] itself, was then monitored using spectroscopic marker emission measurements at λ = 877.4 nm {Ba[6 s 5 d ( 1 D 2 )] → Ba[6 s  2 ( 1 S 0 )]}, λ = 791.1 nm {Ba[6 s 6 p ( 3 P 1 )] → Ba[6 s  2 ( 1 S 0 )]} and λ = 553.5 nm {Ba[6 s 6 p ( 1 P 1 )] → Ba[6 s  2 ( 1 S 0 )]} following energy transfer by collision and energy pooling.  As in previous investigations with other noble gases, first-order rate coefficients for the emission profiles at λ = 553.5 nm, 791.1 nm and 877.4 nm, which demonstrate exponential decay, were found to be in the ratio 2 : 1 : 1 in the long-time regime.  These ‘long times’, typically 1–2 msec, may be contrasted particularly with the mean radiative lifetimes of Ba[6 s 6 p ( 1 P 1 )] (τ e  = 8.37 ± 0.38 ns) and Ba[6 s 6 p ( 3 P 1 )] (τ e  = 1.2 ± 0.1 μs).  A computerised kinetic model is presented to account for these emission profiles in the ‘long-time’ domain.  The decay coefficients resulting from these measurements are used to describe quantitatively the collisional and diffusional processes undergone by Ba( 3 D  J  ) with Ne and Ar, which are considered within the context of all the noble gases.  Particular attention is given to the collisional removal of Ba( 3 D  J  ) by Ba( 1 S 0 ) where all rate measurements, which have hitherto employed a variety of vapour density data for atomic barium at elevated temperatures, are normalised to common vapour pressure data.  Finally, an estimate is made of the mean radiative lifetime, τ e ( Ba  3 D 1 ) = 1.5 ± 0.2 ms.

zeitschrift für physikalische chemie

The Collisional Behaviour of Ba[6 s 5 d ( 3 D  J  )] Generated Following Pulsed Dye-Laser Excitation at λ  = 553.5 nm {Ba[6 s 6 p ( 1 P 1 )] ← Ba[6 s  2 ( 1 S 0 )]} in the Presence of Noble Gases and Ground State Atomic Barium by Atomic Spectroscopic Marker Emission Measurements in the Time-Domain