Investigation of the molecular chemiluminescence SrCl(A²Π_1/2,3/2, B²Σ⁺ → X²Σ⁺) and the atomic resonance fluorescence Sr(5³P₁ → 5¹S₀) in the time‐domain following the pulsed dye laser generation of Sr(5³ P_J) in the presence of CH₂Cl₂

Abstract

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

Determination of the Branching Ratios of CaBr(A2Π1/2,3/2, B2Σ+) Resulting from the Reaction of Ca[4s4p (3PJ)] with CH3Br by Time-Resolved Atomic Emission and Molecular Chemiluminescence Following Pulsed Dye-Laser Excitation of Atomic Calcium

“…As in related investigations on branching ratios for reactions of Ca( 3 P J ) with CH 3 F [20] and CH 3 Cl [21], and also Sr[5s5 p( 3 P J )]with halides in the timedomain [23][24][25][26][27], the integration of the appropriate rate equations leading to the intensities of atomic and molecular states are presented here without immediate correction for the response of the optical system at different wavelengths and the electronic gain of the photomultiplier at different operating voltages but these corrections are included in obtaining the final values of the integrated intensities. As in related investigations on branching ratios for reactions of Ca( 3 P J ) with CH 3 F [20] and CH 3 Cl [21], and also Sr[5s5 p( 3 P J )]with halides in the timedomain [23][24][25][26][27], the integration of the appropriate rate equations leading to the intensities of atomic and molecular states are presented here without immediate correction for the response of the optical system at different wavelengths and the electronic gain of the photomultiplier at different operating voltages but these corrections are included in obtaining the final values of the integrated intensities.…”

“…In contrast to previous measurements on Ca(4 3 P J ) + CH 3 X in the timedomain [16][17][18][19], the present system requires a combination of the comparisons of time-dependences for atomic and molecular emissions together with determinations of integrated intensities using an optically calibrated system [20,21,[23][24][25][26][27]. Ca[4s4 p( 3 P 1 )] was generated by the pulsed dye-laser excitation (10 Hz) of calcium vapour at elevated temperature (T = 940 K) at λ = 657.3 nm {Ca[4s4 p( 3 P 1 )] ← Ca[4s 2 ( 1 S 0 )]} in the presence of methyl bromide and excess helium buffer gas in a slow flow system, kinetically equivalent to a static system.…”

“…Those measurements may be contrasted to analogous later investigations in the time-domain on the reactions Sr(5 3 P J ) [23][24][25][26][27], 1.807 eV above the 5s 2 ( 1 S 0 ) ground state, following pulsed dye-laser excitation of atomic strontium in the presence of various halides which did yield molecular electronic product branching ratios. This development for collisions of Sr(5 3 P J ) arose from improvements in data capture and optical calibrations [23][24][25][26][27]. In this paper, this general approach [23][24][25][26][27] is used to characterise molecular electronic branching ratios yielding CaBr(A 2 Π 1/2,3/2 , B 2 Σ + ) following the reactions of Ca(4 3 P J ) with CH 3 Br.…”

“…This development for collisions of Sr(5 3 P J ) arose from improvements in data capture and optical calibrations [23][24][25][26][27]. In this paper, this general approach [23][24][25][26][27] is used to characterise molecular electronic branching ratios yielding CaBr(A 2 Π 1/2,3/2 , B 2 Σ + ) following the reactions of Ca(4 3 P J ) with CH 3 Br. The results are compared with related results for reactions of Ca(4 3 P J ) in molecular beams, with some very recent branching ratio measurements on Ca(4 3 P J ) with CH 3 F and CH 3 Cl in the time-domain [19,20] and with branching ratio measurements for Sr(5 3 P J ) with halides in the timedomain [22][23][24][25][26], particularly the production of SrBr(A 2 Π 1/2,3/2 , B 2 Σ + ) from the reactions of Sr(5 3 P J ) with CH 2 Br 2 [24].…”

Time-resolved studies of the A2Π and B2Σ states of SrH by laser spectroscopy

“…In recent years, results for the developments in time-resolved laser spectroscopy have been used in the field of collision dynamics. Castano and co-workers [20][21][22][23][24] and several others have made large contributions in this field.…”