Electronic Energy Distribution in SrF by Investigation of the Molecular Chemiluminescence SrF(A²II_1/2,3,2B²Σ⁺ → X²Σ⁺) and the Atomic Resonance Fluorescence Sr(5³P₁‐5¹S₀) in the Time‐Domain following the Pulsed Dye Laser Generation of Sr(5³P_J) in the presence of CH₃F

Abstract

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.

The Collisional Behaviour of Ba[6s5d(3DJ)] Generated Following Pulsed Dye-Laser Excitation at λ = 553.5 nm {Ba[6s6p(1P1)] ← Ba[6s2(1S0)]} in the Presence of Noble Gases and Ground State Atomic Barium by Atomic Spectroscopic Marker Emission Measurements in the Time-Domain

“…This was used with the S20 p.m. tube (E.M.I., 9797B). Similar photomultiplier gating circuitry reported in previous investigations [19][20][21] was used with all detection systems described here to eliminate the effect of scattered light from the laser initiation pulse. Typically, a reverse pulse of 100 Volt of varied duration was applied across the 5th.…”

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

“…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.…”