THE GOAL OF THIS PROPOSAL IS TO DEVELOP A PAH SPECTRAL AND BAND-RATIO LIBRARY THAT CAN BE USED BY THE ASTRONOMICAL COMMUNITY AS A QUANTITATIVE DIAGNOSTIC TOOL FOR DETERMINING THE PAH SIZE AND CHARGING FROM THE OBSERVED BAND RATIOS OF THE PAH EMISSION FEATURES AT 6.2 7.7 AND 11.3 MICRON (I.E. I_6.2/I_7.7 I_11.3/I_7.7). THIS TOOL WILL ALSO PROVIDE INSIGHT INTO THE PHYSICAL CONDITIONS (E.G. THE INTENSITY AND HARDNESS OF THE RADIATION FIELD THE ELECTRON DENSITY) IN THE REGIONS WHERE THE PAH EMISSION IS SEEN. TO ACHIEVE THIS WE WILL CALCULATE THE EMISSION SPECTRA AND BAND RATIOS FOR BOTH NEUTRAL AND IONIZED PAHS OF A WIDE RANGE OF SIZES EXPOSED TO STARLIGHT OF A WIDE RANGE OF INTENSITIES AND OF A WIDE RANGE OF SPECTRAL SHAPES. WE WILL CREATE A LIBRARY OF PAH MODEL EMISSION SPECTRA AND MODEL BAND RATIOS AND GENERATE A SERIES OF DIAGRAMS OF I_6.2/I_7.7 VS. I_11.3/I_7.7. THE "LIBRARY" AND THE BAND-RATIO DIAGRAMS WILL BE MADE PUBLICLY AVAILABLE. TO DEMONSTRATE THE EFFECTIVENESS OF THE BAND-RATIO DIAGRAMS AS A DIAGNOSTIC TOOL WE WILL APPLY THE MODEL I_6.2/I_7.7 VS. I_11.3/I_7.7 DIAGRAMS TO INFER THE PAH SIZE AND IONIZATION FRACTIONS AS WELL AS THE PHYSICAL CONDITIONS OF A WIDE VARIETY OF GALACTIC AND EXTRAGALACTIC REGIONS STARTING WITH THE SIMPLEST GALACTIC HIGH-LATITUDE CLOUDS AND REFLECTION NEBULAE TO EXTRAGALACTIC SYSTEMS OF EVER-INCREASING COMPLEXITY FROM NORMAL STAR-FORMING GALAXIES TO LOW-LUMINOSITY ACTIVE GALAXIES QUASARS ELLIPTICAL GALAXIES AND STARBURST GALAXIES. THE PROPOSED RESEARCH WILL MAKE USE OF ARCHIVAL DATA FROM NASA SPACE ASTROPHYSICS MISSIONS (E.G. ISO SPITZER) THEREBY INCREASING THE SCIENTIFIC RETURN ON THOSE MISSIONS. THE PAH SPECTRAL AND BAND-RATIO LIBRARY AND PARTICULARLY THE I_6.2/I_7.7 VS. I_11.3/I_7.7 DIAGRAMS WILL PROVIDE THE ASTRONOMICAL COMMUNITY WITH AN EFFECTIVE TOOL FOR QUANTITATIVELY STUDYING PAHS IN VARIOUS ASTROPHYSICAL REGIONS. IT IS THEREFORE DIRECTLY RELEVANT TO THE RESEARCH OBJECTIVES OF ADAP AND SUPPORTS NASA'S STRATEGIC OBJECTIVE TO "DISCOVER HOW THE UNIVERSE WORKS AND HOW IT BEGAN AND EVOLVED" (OBJECTIVE 1.6 OF THE 2014 NASA STRATEGIC PLAN).