Conservation of the Kr+(2P1/2) state in the reactive quenching of Kr(5s′[1/2]) atoms by halogen-containing molecules

Abstract

Absolute cross sections for photoionization of excited rare gas atoms near threshold: Ar*(4p 3 D 3), Kr*(5p 3 D 3), and Xe*(6s 3 P 0) AIP Conf.The second metastable state of Kr, 5sЈ͓1/2͔ 0 , was generated from the first metastable state, 5s͓3/2͔ 2 , by optical pumping in a flow reactor. Under optimum conditions, the entire Kr͑5s͓3/2͔ 2 ͒ concentration could be removed with more than 40% conversion to the Kr͑5sЈ͓1/2͔ 0 ͒ state, which is stable in He carrier gas. The Kr͑5sЈ͓1/2͔ 0 ͒ and Kr͑5s͓3/2͔ 2 ͒ states have the Kr ϩ ͑ 2 P 1/2 ͒ and Kr ϩ ͑ 2 P 3/2 ͒ ion cores, respectively, as do the Kr ϩ X Ϫ (D) and Kr ϩ X Ϫ (B,C) states. The reactions of a series of fluorine-, chlorine-, and bromine-containing molecules, RX, with the Kr͑5sЈ͓1/2͔ 0 ͒ and Kr͑5s͓3/2͔ 2 ͒ atoms were studied by measuring the total quenching rate constants and by observing the KrX(B,C,D) product emission spectra. In contrast to the Kr͑5s͓3/2͔ 2 ͒ atoms, which give KrX͑B and C͒ products, the Kr͑5sЈ͓1/2͔ 0 ͒ atoms have a high propensity to give KrX(D) plus a lesser amount of KrX(B), depending on the reagent, as products. Discrimination against KrX(C) formation by reactions of Kr͑5sЈ͓1/2͔ 0 ͒ atoms is severe. The reactions with F 2 , NF 3 , and N 2 F 4 exhibit the highest conservation of the Kr ϩ ͑ 2 P 1/2 ͒ core, and these Kr͑5sЈ͓1/3͔ 0 ͒ reactions give Ͼ70% KrF(D). The total quenching constants of Kr͑5sЈ͓1/2͔ 0 ͒ atoms generally are equal to those for Kr͑5s͓3/2͔ 2 ͒, but the branching fractions for KrX* formation from Kr͑5sЈ͓1/2͔ 0 ͒ atoms generally are smaller than for Kr͑5s͓3/2͔ 2 ͒ atoms. A correlation diagram based on conservation of Kr ϩ ion-core state and ⍀ϭ0 Ϫ is developed to discuss these trends and the reactions of the Xe͑6sЈ͓1/2͔ 0 and 6s͓3/2͔ 2 ͒ atoms. Due to the absence of KrX(C -A) emission from the Kr͑5sЈ͓1/2͔ 0 ͒ atom reactions, the KrX(B -A) and Kr(D -A) transitions could be observed and the radiative branching ratios to the X and A states were assigned. © 1996 American Institute of Physics. ͓S0021-9606͑96͒00536-3͔ ͗ f V ͘ϭ0.6-0.7, the alignment of the rare gas halide product molecule, 3,4 and the ϳ100 Å 2 reactive cross section are typical of harpooning dynamics. 5 The corresponding Xe͑6s͓3/2͔ 1 ͒ and Kr͑5s͓3/2͔ 1 ͒ resonance atoms 6 exhibit the same reaction dynamics as the ͓3/2͔ 2 metastable atoms with X 2 molecules. For polyatomic halogen-containing molecules, RX, with smaller electron affinities than X 2 molecules, the distance at which the diabatic covalent and ion-pair potentials interact becomes smaller and ⌫ RgX* becomes less than unity, due to the competition with excitation transfer to RX* states. The ͓3/2͔ 2,1 states of Xe* and Kr* have the ground state ion core and reactions with RX molecules correlate to the rare gas halide ͑B,⍀ϭ1/2 and C,⍀ϭ3/2͒ product states, which also have the 2 P 3/2 ion-core state. The fraction of B and C molecules for different RX reagents and for Xe* vs Kr* is an aspect of the ͓3/2͔ 2,1 atom reactions that remains to be explained. In the present work, we have studied the third excited state, 5...

Molecular beam study of the collisions of state-monitored, metastable noble gas atoms with O2(X 3Σg−)

“…1͑e͒ Some degree of ion-core nonconservation has been seen for Kr* luminescent reactions with halogen-containing molecules. 36 Our preliminary value of about 125 Å 2 for Xe*( 3 P 0 ) is the largest cross section we have measured with our new technique. Also, our experiment for Kr* with the Kr*ϩH 2 O→KrϩOH*ϩH monitor confirms the recent observation by Setser and co-workers 36 that this reaction occurs exclusively for Kr*( 3 P 0 ).…”

“…5. Very recently, Setser and co-workers 36 reported that the Kr*ϩH 2 O→KrϩOH*ϩH reaction originates entirely from Kr*( 3 P 0 ). We undertook one experiment on Kr*ϩO 2 using the aforementioned reaction as a monitor.…”

“…Setser and co-workers find strong evidence for ion-core relaxation in Xe* reactions, 1͑c͒ and to a lesser extent in some Kr* reactions as well. 36 If the ion-pair intermediate approach is valid, then a more realistic model is the Ionic-Intermediate-Curve Crossing Model of Fisher and co-workers. 12 We have applied this model to the Ar*( 3 P 2 )ϩO 2 reaction, and the results are given in Fig.…”

Multidimensional steric effect for the XeBr∗ (B, C) formation in the oriented Xe∗(P32, MJ=2)+oriented CF3Br reaction

“…The nonclosed shell of Rg + gives rise to two different excited rare gas halide product states, RgX ‫ء‬ ͑B,⍀ =1/ 2͒ and RgX ‫ء‬ ͑C,⍀ =3/ 2͒, which correlate with Rg + ͑ 2 P 3/2 ͒ and X − ͑ 1 S 0 ͒. The RgX ‫ء‬ formation is known to proceed via the "harpoon" mechanism [22][23][24][25][26][27] such as the metal halide MX formation in the reaction of alkali-metal atoms M, for which steric effects have been widely studied using the oriented molecules. [1][2][3][4][5][6][7][8][9][10][11][12][13][16][17][18] For the KI formation in the K + CF 3 I reaction system, it has been reported that the molecular orientation exerts an influence on only the angular distribution of KI with the comparable reaction probability at the two ends.…”

Multidimensional steric effect for the XeF* (B, C) formation in the oriented Xe* (3P2, MJ= 2) + oriented NF3reaction

“…The non-closed shell of Rg + gives rise to two different excited rare gas halide product states, RgX* (B, O = 1/2) and RgX* (C, O = 3/2), that correlate with Rg + ( 2 P 3/2 ) and X À ( 1 S 0 ). The RgX* formation is known to proceed via the ''harpoon'' mechanism [24][25][26][27][28][29] like the metal halide MX formations in the reactions of alkali-metal atoms M, for which steric effects have been widely studied using the oriented molecules. [1][2][3][4][5][6][7][8][9][10][11][12][18][19][20][21] For the KI formation in the K + CF 3 I reaction system, it has been reported that the molecular orientation exerts an influence on only the angular distribution of KI with comparable reaction probability at the two ends.…”