Kinetic investigation of the time-resolved atomic fluorescence Ca(4 3P 1→4 1S 0) and molecular chemiluminescence CaF(A 2Π→X 2Σ +) following the pulse-dye laser generation of Ca(4 3P J) in the presence of CH 3F

Abstract

A time-resolved investigation is presented of the collisional behaviour of the optically metastable, electronically excited Ca(4s4p( 3P J)), 1.888 eV above its 4s 2( 1S 0) electronic ground state, with the molecule CH 3F. Ca(4s4p( 3P 1)) was generated by the pulsed dye-laser excitation of calcium vapour at an elevated temperature in the presence of CH 3F and excess helium buffer gas and the resulting atomic fluorescence at the resonance wavelength (λ=657.3 nm, Ca(4s4p( 3P 1))→Ca(4s 2( 1S 0)+ hv)) was monitored, following rapid Boltzmann equilibration within the Ca(4 3P J) spin-orbit manifold, using boxcar integration. The electronically excited atom exhibited exponential decay profiles which were characterized quantitatively. Time-resolved chemiluminescence was also monitored under identical conditions for the CaF(A 2Π→X 2Σ +) system, principally via the (0,0) transition, on account of Franck—Condon limitations. This molecular emission exhibits decay profiles which are also exponential in form, characterized by decay coefficients which are equal in magnitude to those from Ca(4 3P J), and arising from chemiluminescence following the direct reaction ▪ Chemiluminescence from CaF(B 2Σ +) via the B 2Σ +−X 2Σ + system, which is also thermochemically accessible on collision between Ca(4 3P)+CH 3F, was not detected. The laser-induced fluorescence spectrum, CaF(A 2Π 1 2 , 3 2 −X 2Σ +), following excitation of the X 2Σ + ground state, where the A 2Π 1 2 , 3 2 spin-orbit components were, of course, resolved, was also monitored following the reaction of Ca(4 3P J)+CH 3F. However, these spin-orbit components could not be resolved in chemiluminescence on account of intensity restrictions at the optical resolution required. These results for reaction leading to CaF(A 2Π) with the subsequent chemiluminescence are compared with analogous collisional processes for Ca(4 3P J) involving oxygen, hydrogen, chlorine and bromine atom abstraction processes in the time-domain, and halogen atom abstraction studied in molecular beams.