A fluorescence monitor method for measuring effective absorption coefficients of molecular rovibronic transitions using tunable dye laser excitation: The case of absorber linewidth narrower than the laser linewidth applied to H2CO

Abstract

A technique for measuring ’’effective’’ absorption coefficients is described. It circumvents deviations from Beer’s law caused when the excitation source bandwidth is larger than the absorber bandwidth. The technique employs a fluorescence cell placed after an absorption cell to selectively monitor absorption in the center region of the source line. Model calculations relating the fluorescence intensity to source and absorber line shapes indicate that this method should yield linear Beer’s law plots for moderate values of k0Nl and α, where α is the ratio of the source bandwidth to the absorber bandwidth. This technique has been applied to a number of single rotational levels in the 410 transition of the H2CO ? 1A2←? 1A1 system using pulsed, tunable dye laser excitation. The effective absorption coefficients determined experimentally have been compared to the theoretically calculated absorption coefficients.