Dynamics of the (CFO)2 Photochemistry: Pressure Dependence.

SALAS, JUANA; BURGOS PACI, MAXIMILIANO; ANZANI, ANGEL FEDERICO; BERASATEGUI, MATIAS ; ARGUELLO, GUSTAVO

Lille, Francia

Simposio; The 25th International Symposium on Gas Kinetics and Related Phenomena; 2018

Introduction. Oxalylfluoride has an allowed electronic Â1 Au ← X1 Ag transition with anabsorption band located at about 308 nm.1,2 For excitation energies above this wavelengththe fluorescence efficiency decreases, and the photochemical decomposition takesplace.3,4 In the present work we explore the dynamics of fluorescence and photodisociationresolved in time, in the presence of different quenchers.Experimental. The photolysis was initiated with a Ne: YAG at his fourth harmonic (266nm, 0,400 W). The (FCO)2 absorption cross-section at this wavelength is ≈ 1 × 10-19 cm2molecule-1.4 The IR radiation was collected with a concave golden mirror and focusedthrough a filter (2000 ? 2400 cm-1) to an InSb detector. To register the UV-Visiblephosphorescence a monochromator connected to a photomultiplier was used (resolutionof 0.1 nm). For the spectroscopic measurement, a FTIR and a fluorometer were used.Results. Under theexperimental conditions,several processes may occur:(CFO)2* → (CFO)2 + hν(UV-Vis)(CFO)2* → 2 FCO* → F + CO*(CFO)2* → CO* + CF2OCO* → CO + hν(IR)The phosphorescencespectrum is presented in Figure1.a. We follow the band at356.7 nm to register thetemporal decay of the â3Au. Inthe presence of inert gases (O2and Ar) only a decrease in life-time was observed, whereas in the presence of more complex molecules an increase inthe total emission takes place with the increase in pressure (the test was carried out withgases such as CO, CH3C≡N and cyclohexane). Figure 1.b. presents the time-resolvedfluorescence for the band at 356.7 nm at different pressures of (CFO)2.Figure 1.c. presents the FTIR spectrum of the final product of the photolysis. With the IRfilter, only the CO* (vibrational excited) emissions region is measured. Figure 1.d. presentsthe time-dependence of the IR emission bands. No pressure dependence was observedwhen an inert gas is loaded, but the IR signal decrees drastically with the increase ofcomplex molecules pressure.Conclusion. Complex molecules could determine the phosphorescence or rupture yieldonce the (CFO)2 molecule is excited by laser radiation at 266 nm. This effect is due to thecollisional relaxation suffered by the (CFO)2*.