Data on vibrational spectra of polycycic aromatic hydrocarbons in gas phase are of considerable interest for solving the astrophysical problems. Results of experimental and theoretical investigations of spectral characteristics: positions, widths, absorption cross-sections and oscillator strengths of anthracene molecule bands in the 800-3200 cm' region are given. Comparison of experimental and calculated intensity distribution in a separate absorption band of anthracene vapors shows that a decisive factor in forming a profile is free rotation of molecules.

Sensors are designed and offered for determining concentrations of luminescent impurities in different technological media. The sensors consist of quartz monoblock with a replica of concave diffraction grating and joined optical fibers. This allow to combine collimating, dispersing and focusing propeties necessary for a spectral analysis in single optical element. Comparison of a signal level of a detector responding to a fluorescence intensity of a monitored substance with a signal in a comparison channel permits to monitor concentration in terms of concentration dependence determined beforehand.Nowadays devices based on fiber optics1 are successfully used for remote monitoring hardly accessible isolated objects and different media as well as for analyzing the run of different technological proccesses. An apparatus located on board of a research ship for monitoring chlorophyll content in sea water using laser-induced fluorescence for an analysis is described in the work2. A fluorescent signal is fed on board of a ship using the same light waveguide as for transmitting an exciting radiation into sea medium. A set of experiments2 has shown a possibility of recording chlorophyll concentration in real time and in the case of laser excitation the signal of water-medium Raman scattering serves as an internal standard on the basis of which the chlorophyll fluorescence may be calibrated.However, optical circuits of such devices2 are rather intricate and are a monochromator with a plane grating, two concave mirrors and additional mirror-lens systems. The usage of such devices as sensors is difficult due to the necessity of continuous control and alignment. Moreover, the intricacy of devices does not allow to launch their mass production that is necessary for realizing diagnostic and monitoring systems.We have designed and offered sensors for determining luminescent impurities in sewage water and different technological media. Sensors consist of a glass or quartz monoblock ( Fig. 1(2)) to one end of which the input and output fibers are joined ( Fig. 1(1,4,6,7)) and on the other end is located a replica of a concave diffraction grating (3) with a groove geometry ensuring minimal energy losses. The principal novelty of the offered sensors is the usage of such a grating-block allowing to combine collimating, dispersing and focusing properties necessary for a spectral analysis in a single optical element. An evident advantage of the construction is a monoblock ensuring stability to disalignment and absolute O-8194-1504-9/94/$6.OQ SPIE Vol. 2205 High-Resolution Molecular Spectroscopy (1993)! 515 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 06/24/2016 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspx

Results of complex investigating the conditions of appearing and objective laws of exhibiting a structural spectrum of anthracene-vapour fluorescence are presented. The data show that the usage of the suggested procedure permits to obtain such highly-resolved spectra (in heated vapours of aromatic compounds) as those in the case of deep cooling in matrices and molecular jets.As a rule, spectra of complex multi-atomic molecules of aromatic compounds in a gas phase have no fine structure1. However,the narrowing of radiation bands and the appearance of individual quasi-lines against diffuse bands are observed in radiation spectra of some aromatic molecules in the case of specific conditions of excitation.Previous researchers have noted that a quasi-linear spectrum of vapour fluorescence is observed in exciting only in the region of a 0-0 transition.Our investigations have shown the existence of regions of excitation wavelengths referred as excitation zones where fluorescence spectra retain their quasi-linear structuie27. The most complete experimental and theoretical investigations of quasi-linear spectra were perfonned for anthracene. Fig. 1 shows a quasilinear spectrum of anthracene-vapour fluorescence.

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