Non-linear Pressure Dependence of Fluorescence Decay Rate for Concentration Measurement of Formaldehyde using Laser-Induced Fluorescence
Details
Fluorescence lifetime of formaldehyde excited at 352nm A-X 4^1_0 band was measured as a function of pressure of bath gas: He, N_2, O_2, CO_2, and CH_3OCH_3 (DME). Temperature dependence of lifetime between room temperature and 375K was also examined. In this study we proposed "two-step decay model", which successfully reproduced the non-linear pressure dependence of the inverse lifetime. This model assumes that the optically excited formaldehyde undergoes a reversible collision transfer to a state of higher spontaneous decay rate along with direct collisional and spontaneous deactivation pathways. It was confirmed that the lifetime in a bath gas mixture can be reproduced by this model with the rate constants individually obtained as linear combinations of the bath gas contributions. The temperature dependence is expressed by giving activation energies for the constants in this model formula.
