Fluorescence and Induced Phosphorescence of Formaldehyde in Solid Lowhyphen;Temperature Solutions

摘要

The absorption and emission spectrum of formaldehyde was studied in xenon, krypton, and sulfur hexafluoride and without matrix between 20deg; and 200deg;K in the region of 2600ndash;6000 Aring;. Matrix isolation of formaldehyde, even atMsol;R1000, is dependent on solvent. The SF6yields more than 99percnt; isolation, xenon 90percnt;, and krypton only 50percnt;. TheS1larr;S0absorption is broad in all cases, and the systemT1larr;S0is too weak to be studied in detail. Strong emission in the 3800ndash;5400hyphen;Aring; region is observed. The emission spectrum is independent of the exciting frequency between 2500 and 3500 Aring;. In pure formaldehyde it is due to fluorescence ofS1rarr;S0only, and in matrices it is due to simultaneous and overlapping fluorescence and phosphorescence. The fluorescence resembles the gashyphen;phase spectrum and is analyzed accordingly. Phosphorescence is caused by intersystem crossing. The phosphorescence yield increases with solvent polarizability and decreases reversibly with increasing temperature until diffusion occurs. Phosphorescence yields are always smaller than 5percnt; of fluorescence. The lifetime of phosphorescence is 0.23 sec in xenon, 1.1 sec in krypton, and 0.63 sec in SF6. The phosphorescence spectrum is deduced from the intensity of the long lifetime component, and also from the reversible temperaturehyphen;dependent component of the emission intensity.