Excitation, emission, and synchronous fluorescence for astrochemical applications: Experiments and computer simulations of synchronous spectra of polycyclic aromatic hydrocarbons and their mixtures
Synchronous fluorescence spectroscopy is a variation of the fluorescence technique for detection and characterization of many single ring aromatic organic molecules, polycyclic aromatic hydrocarbons, and fluorescent amino acids among other molecules. To our knowledge this technique has not been used in space exploration. In order to demonstrate the utility of this technique for planetary and astrochemical applications, we present several laboratory experiments and computer simulations with pure samples and mixtures. Computer deconvolution of experimental excitation and emission fluorescence bands is presented and used to generate synchronous spectra. The computer simulation successfully predicts the number of synchronous fluorescence (SF) bands, band shapes, and band maximum wavelengths for any constant wavelength difference (Δλ). To test the simulation, emission, excitation, and synchronous spectra were obtained for anthracene in n-hexane. Excellent agreement is obtained reproducing and finding the origin of the experimental SF bands for values of Δλ between 2 and 100. The excitation, emission, and synchronous (Δλ = 10) spectra of toluene, aniline, naphthalene, acenaphthene, pyrene, and anthracene are obtained. Excitation of a mixture of the six compunds at three wavelengths (249, 266, and 355 nm) produce fluorescence emission spectra identifying some compounds. The synchronous spectrum (Δλ = 10) of the same mixture is presented and assigned based on the synchronous bands of the individual compounds. The synchronous fluorescence technique and the computer simulation method are proposed to complement other techniques in the analysis of fluorescent samples from comets, as well as in missions to planets and satellites of the solar system.