A time-resolved investigation is presented of the electronic energy distribution in SrI following the collision of the optically metastable strontium atom, Sr [5s5p(3PJ)], with the molecule CF3I. Sr[5s5p(3PJ)], 1.807 eV above its 5s2(1S0) electronic ground state, was generated by pulsed dye-laser excitation of ground state strontium vapour to the Sr(53P1) state at , λ =689.3 nm {Sr(53P1←51S0)} at elevated temperature (840 K) in the presence of excess helium buffer gas in which rapid Boltzmann equilibration within the 53PJ spin-orbit manifold takes place. Time resolved atomic emission from Sr(53P1→51S0) at the resonance transition and the molecular chemiluminescence from SrI(A2∏1,2,3/2,B2∑+→X2∑+) resulting from reaction of the excited atom with CF3I were recorded and shown to be exponential in character. SrI in the A2∏1/2,3/2 (172.5, 175.4 kJ mol-1) and B2∑+ (177.3 kJ mol-1) states are energetically accessible on collision by direct-I-atomic abstraction between Sr(3P) and CF3I. The first-order decay coefficients for the atomic and molecular emissions are found to be equal under identical conditions and hence SrI(A2∏1/2,3/2, B2∑+) are shown to arise from direct I- atom abstraction reactions. The molecular systems recorded were SrI (A2∏1/2→X2∑+, Δv=0, λ=694 nm), SrI(A2∏3/2→X2∑+, Δv=0, λ=677 nm) and SrI(B2∑+→X2∑+) (Δv=0, λ=674 nm), dominated by the Δv=0 sequences on account of Franck-Condon considerations. The combination of integrated m61ecular and atomic intensity measurements yields estimates of the branching ratios into the specific electronic states, A1/2, A3/2 and B, arising from Sr(53PJ)+CF3I which are found to be as follows: A1/2,1.2 × 10-2; A3/2, 6.7 × 10-3; B, 5.1 × 10-3 yielding ∑SrI(A1/2+A3/2+B)=2.4 × 10-2. As only the X, A and B states SrI are accessible on reaction, assuming that the removal of Sr(53PJ) 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 on various halogenated species resulting from reactions of Sr(53PJ), together with analogous chemiluminescence studies on Sr(3PJ) and Ca(43PJ) from molecular beam measurements.

Time-resolved investigations of the atomic resonance fluorescence Sr(53P1 -5'So) and the molecular chemiluminescence from SrCl(A2n1/z,3/2, B 2 8 + --t X2Z1) are reported following the reaction of the electronically excited strontium atom, S r ( 5~5 p (~P j ) ) , 1.807 eV above its 5s2(lS0) electronic ground state, with CHZC12. The optically metastable strontium atom was generated by pulsed dye-laser excitation of ground state strontium vapor to the Sr(53P1) state at A = 689.3 nm ( S I -(~~P~ + 5lSo)) a t elevated temperature (850 K) in the presence of excess helium buffer gas in which rapid Boltzmann equilibration within the 5 3 P~ manifold takes place. Sr(53P~) was then monitored by time-resolved atomic fluorescence from S I -(~~P~) at the resonance wavelength together with chemiluminescence from electronically excited SrCl resulting from reaction of the excited atom with CH2C12. The molecular systems recorded in the time-domain were SrC1(A2n1/2 + X 2 X + ) (Au = 0, A = 674 nm), SrC1(A2113/z -X 2 Z + ) (Au = 0, A = 660 nm), and SrC1(B28+ -X 2 2 + ) ( A u = 0, A = 636 nm). Both the A211 (179.0 kJ mol-l) and B2Z+(l88.O) kJ mol-l) states of SrCl are energetically accessible on collision between Sr(3P) and CH2Cl2. Exponential decay profiles for both the atomic and molecular (A,B -X) chemiluminescence emission are observed and the first-order decay coefficients characterized in each case. These are found to be equal under identical conditions and hence SrC1(A2n,B2Z+) are shown to arise from direct C1-atom abstractions on reaction with this halogenated species. The combination of integrated molecular and atomic intensity measurements, coupled with optical sensitivity calibration, yields estimations of the branching ratios into the A1/2,3/2, B, and X states arising from S r ( 5 3 P~) + CHzClz which are found to be as follows: Allz, 3.0 X yielding 8SrCl(Au2 + A312 + B) = 5.1 X As only the X, A and B states of SrCl are accessible on reaction, this indicates an upper limit for the branching ratio into the ground state of 0.995. The present results are compared with previous time-resolved measurements on SrF, CI, Br(A2n,B2Zt -X2C+) that we have reported on various halogenated species and with analogous chemiluminescence studies on Sd3P) with other halides obtained from molecular beam measurements. The results are further compared with those from a series of previous analogous investigations in the time-domain we have presented of molecular emissions from CaF, C1, Br, I (A,B ~ X) arising from the collisions of Ca(43P~) with appropriate halides and with branching ratio data for Ca(43Pj) obtained in beam measurements. 0 1995

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A kinetic study is presented of the electronic energy distribution in SrF following the reaction of the electronically excited strontium atom, Sr (5s5p('P ,)), 1.807 eV above its 5s2('S0) electronic ground state, with CH,F. This optically metastable atom was generated by pulsed dye-laser excitation of ground state strontium vapour to the Sr(53P,) state at J. = 689.3 nm (Sr(53P,+5fS,)) at elevated temperature (850 K) in the presence of excess helium buffer gas in a slow flow system, kinetically equivalent to a static system. The decay of Sr(5'P,,) was then monitored by time-resolved atomic fluorescence from Sr (53P,) at the resonance wavelength following rapid Boltzmann equilibration within the 3PJ spin-orbit manifold. Electronically excited SrF resulting from reaction of the excited atom with CH3F was also recorded in the time-domain via the systems SrF(A2III,,+XZZ+) ( A u = O , I = 6 6 2 n m ) , SrF(A2113,2+X2Zt) ( A u = O , J.=652nm) and SrF(B2Z+-X2Ct) ( A u = O , /I = 579 nm). The A 2 n (181.9 kJ mol-I) and B2Z + (206.6 kJ mol-I) states of SrF are both energetically accessible on collision between Sr('P) and CH,F. Both the atomic and molecular (A,B-X) chemiluminescence emissions are shown to be exponential in form and characterised by first-order decay coefficients which are found to be equal under identical conditions within experimental error. SrF(A2n) and SrF(B2Z ' ) are thus both shown to arise from direct reaction with CH,F. Further, the combination of integrated atomic and molecular intensity measurements, coupled with optical sensitivity calibration, enables estimates of the branching ratios into the A,,,, ,*, B and X states arising from Sr(5'PJ)+CH3F to be made yielding the following results: A,,,, 6 . 4~ lo-'; A,,,, 1 . 5~1 0 --~; B, 1.1 x X, 0.992. The results obtained here are compared with analogous chemiluminescence studies on Sr (3P) with other halides obtained from molecular beam measurements and with previous kinetic measurements on SrC1, Br(A2n, B2X+ -X 2 Z + ) that we have reported. The results are also compared with those from a series of investigations we have presented from time-domain investigations of molecular emissions from CaF, Cl, Br, I (A,B-X) arising from the collisions of Ca(43P,) with appropriate halides.

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