Time-Resolved Investigation of the Molecular Chemiluminescence SrI(A2∏1/2,3,2,B2∑+→X2∑+) and the Atomic Resonance Fluorescence Sr(53P1→51S0) Following The Pulsed Dye Laser Generation Of Sr(53PJ) in the Presence of CF3I

A time-resolved investigation is presented of the electronic energy distribution in SrI following thecollision of the optically metastable strontium atom, Sr [5s5p( 3 P J )], with the molecule CF 3 I. Sr[5s5p( 3 P J )], 1.807 eV above its 5s 2 ( 1 S 0 ) electronic ground state, was generated by pulsed dye-laser excitation of groundstate strontium vapour to the Sr(5 3 P 1 ) state at , λ =689.3 nm {Sr(5 3 P 1 ←5 1 S 0 )} at elevated temperature (840 K) in the presence of excess helium buffer gas in which rapid Boltzmann equilibration within the 5 3 P J spin-orbitmanifold takes place. Time resolved atomic emission from Sr(5 3 P 1 →5 1 S 0 ) at the resonance transitionand the molecular chemiluminescence from SrI(A 2 ∏ 1,2,3/2, B 2 ∑ + →X 2 ∑ + ) resulting from reaction of the excitedatom with CF 3 I were recorded and shown to be exponential in character. SrI in the A 2 ∏ 1/2,3/2 (172.5, 175.4 kJ mol -1 ) and B 2 ∑ + (177.3 kJ mol -1 ) states are energetically accessible on collision by direct-I-atomicabstraction between Sr( 3 P) and CF 3 I. The first-order decay coefficients for the atomic and molecular emissions are found to be equal under identical conditions and hence SrI(A 2 ∏ 1/2,3/2 , B 2 ∑ + ) are shown to arise from direct I- atom abstraction reactions. The molecular systems recorded were SrI (A 2 ∏ 1/2 →X 2 ∑ + , Δv=0, λ=694 nm), SrI(A 2 ∏ 3/2 →X 2 ∑ + , Δv=0, λ=677 nm) and SrI(B 2 ∑ + →X 2 ∑ + ) (Δv=0, λ=674 nm), dominatedby the Δv=0 sequences on account of Franck-Condon considerations. The combination of integratedm61ecular and atomic intensity measurements yields estimates of the branching ratios into the specific electronicstates, A 1/2 , A 3/2 and B, arising from Sr(5 3 P J )+CF 3 I which are found to be as follows: A 1/2 ,1.2 × 10 -2 ; A 3/2 , 6.7 × 10 -3 ; B, 5.1 × 10 -3 yielding ∑SrI(A 1/2 +A 3/2 +B)=2.4 × 10 -2 . As only the X, A and B states SrI are accessible on reaction, assuming that the removal of Sr(5 3 P J ) occurs totally by chemical removal, this yields an upper limit for the branching ratio into the ground state of ca. 98%. The present results are compared with previous time-resolved measurements on excited states of strontium halides that we have reported onvarious halogenated species resulting from reactions of Sr(5 3 P J ), together with analogous chemiluminescence studies on Sr( 3 P J ) and Ca(4 3 P J ) from molecular beam measurements.