Pb 6p Research Articles

A kinetic study of the third order reactions of atomic lead, Pb(6 3P 0) + C 2H 2 + M and Pb(6 3P 0) + C 2H 4) + M

We describe a kinetic study of the overall third order processes Pb + C 2H 2 + M (reaction (1)) and Pb + C 2H 4 + M (reaction (2)) by resonance line absorption measurements on the Pb(6 3P 0) ground state. These atoms were generated by pulsed irradiation and monitored photoelectrically in absorption in the single-shot time-resolved mode at λ = 283.3 nm (Pb(7s( 3P o 1)) ← Pb (6p 2( 3P 0))). Absolute third order rate constants (at 300 K in units of cm 6 molecule −2 s −1) are reported for the following third bodies M: reaction (1), 10 33 k 1 — He (1.3 ± 0.2), N 2 (2.6 ± 0.3), CO 2 (3.9 ± 0.3), CH 4 (5.3 ± 0.6) and SF 6 (4.5 ± 0.5); reaction (2), 10 33 k 2 — He (1.2 ± 0.1), N 2 (4.2 ± 0.3), CO 2 (5.0 ± 0.3), CH 4 (3.7 ± 0.6) and SF 6(5.6 ± 0.3). These data are compared, where possible, with data for analogous reactions of Sn(5 3P 0), Sb(5 4S 3 2 ) and Bi(6 4S 3 2 , and also with rate data for Pb + Pb + M and Pb + O 2 + M.

Reactions of ground state lead atoms Pb(6 3P 0) with alkyl bromides studied by atomic absorption spectroscopy

We present a kinetic study of the collisional removal of ground state lead atoms Pb(6 3P 0) by alkyl bromides. Pb(6 3P 0) was generated by the pulsed irradiation of Pb(C 2H 5) 4 and monitored photoelectrically by resonance line absorption at λ = 283.3 nm (Pb(7s( 3P 0 1)) ← Pb(6p 2( 3P 0))). We report the following second order absolute rate constants k R for the reaction (in cm 3 molecule −1 s −1 at 300 K): CH 3Br, 3.7 ± 0.5 × 10 −15; C 2H 5Br, 5.0 ± 0.5 × 10 −15; CH 2BrCH 2Br, 5.3 ± 0.3 × 10 −14; CH 2Br 2, 1.4 ± 0.2 × 10 −13; CH 3CHBr 2, 6.0 ± 0.5 × 10 −13; HBr, less than 10 −15. The rate constants are discussed in terms of the thermochemical data pertinent to Br atom abstraction and also in terms of a Hammett relationship.

A kinetic study of the third order reactions of atomic lead: Pb(6 3P 0) + O 2 + M and Pb + NO + M

The third order kinetic reactions Pb + O 2 + M (reaction (1)) and Pb + NO + M (reaction (2)) have been studied by atomic absorption spectroscopy of Pb(6 3P 0) following flash photolysis. Pb(6 3P 0) was generated by pulsed irradiation of PbEt 4 in the presence of excess buffer gas (M) and was monitored photoelectrically in absorption in the single shot mode by time resolved attenuation of atomic resonance radiation at λ = 283.3 nm due to the transition Pb(7s( 3P 0 1)) ← Pb(6p 2( 3P 0)). Absolute third order rate constants are reported for reaction (1) for the gases He, N 2, CO, CO 2, CH 4, CF 4, SF 6, C 2H 6, C 2H 2 and C 2H 4. A similar study is also presented for reaction (2) which is usually of the order of 50 – 100 times faster than reaction (1) for a given third body M. On this account, reaction (2) is found to be highly sensitive to impurities of O 2 and a number of the analogous rate constants are less reliable. The rate data are discussed with reference to other atom—molecule recombination processes, to atomic recombination and to the quenching of atomic fluorescence.

Collisional quenching of the spin-orbit states of atomic tin, Sn(5p 23P 2) and Sn(5p 23P 1)

A kinetic study of gaseous tin atoms in the low lying spin-orbit states, Sn(5p 2 3P 1) and Sn(5p 2 3P 2), respectively, 0.210 and 0.425 eV above the (5p 2 3P 0) electronic ground state, is presented. These two optically metastable states, together with the 3P 0 ground state, were generated by the pulsed irradiation of SnMe 4 and monitored photoelectrically in absorption by time-resolved attenuation of atomic resonance radiation. The first absolute rate data for the collisional quenching of these two excited states by the gases Ar, H 2, D 2, O 2 and SnMe 4 are reported and compared with the previously determined analogous data for Pb(6p 2 3P 1,2). The resulting absolute second-order rate constants for both sets of spin-orbit states are discussed within the framework of symmetry arguments based on ( J, Ω) coupling. For the particular case of the quenching of Pb(6 3P 1) by O 2, the kinetic behaviour of both the 3P 1 and 3P 0 states seem to be fully consistent with the rapid establishment of an equilibrium for the near resonant electronic energy exchange processes: Pb(6 3P 1) + O 2(X 3Σ g −) ⇌ Pb(6 3P 0) + O 2(a 1Δ g), Δ E = 105 cm −1.

Calculation of spin orbit relaxation rates by near resonant E → V energy transfer

Abstract This paper calculates the cross sections and their temperature dependences of the collisional relaxation of Pb 6p 2 3 P 2 by D 2 and Te 5p 4 3 P 1, 0 by H 2 . Relaxation of these electronic metastable states can take place by a near resonant E → V energy transfer. The theory considers coupling of initial and final states by long range attractive forces. A calculation based on quadrupole-quadrupole coupling gives a reasonably close estimate of observed rates. The selection rules and limitations of the theory are briefly discussed.