FDM FTIR and Raman Spectral Libraries

• 550 cm-1 to 4000 cm-1, single bounce ZnSe ATR crystal

• 4 cm-1 resolution

• 38.8 to 58.8 degrees angle of incidence (AOI), small increments

• multiangle non-polarized spectra

• multiangle Rp, Rs polarized spectra

The  FDM Multiangle ATR Polymers is a unique spectral library providing a  new perspective on polymer ATR/FTIR spectra.  It is well known that  ATR/FTIR peak positions, shapes and intensities can change as a function  of AOI, especially for the strongest peaks at lower angles. But until  now there have not been any libraries to browse or search spectra  recorded on variable angle ATR/FTIR accessories or spectra recorded on  ATR/FTIR accessories with other AOIs such as 60 degrees.

Multiangle  or Variable Angle ATR spectra have an easy to understand advantage.   Anything done with a fixed angle spectrum can probably be done better  with a  collection of multiangle spectra because there is more  information and signal.

The  library contains three types of ATR spectra: (1) not polarized and (2)  Rp (p-polarized) and (3) Rs (s_polarized). The polarized spectra make it  even easier to see pronounced features with varying AOI. It contains  spectra of resin blocks, adhesives, sealants, gels, and a few simple  paints.

Users  can see what spectra look like at 45 degrees AOI and at higher and  lower angles. At lower angles, many peaks are scanned above and below  their respective critical angles showing users distinctive new features  for searching or quantitation. Users can see how they can revise their  ATR methods to easily attain substantial increases in sensitivity or  simply additional distinctive spectra. At higher angles, spectra run on  the ZnSe crystal resemble those run on a Germanium crystal, which are  more transmission-like.

Scientists  using Variable Angle ATR accessories for thin film analysis and depth  profiling now have reference spectra to match their spectra over a wide  range of angles (38.8 to 58.8 degrees). See the chemical name index.   With the combination of the library, highly sensitive search  algorithms, and the varying AOI, you can identify the spectra of many  materials over a wide range of AOI and polarizations.

Scientists  with a conventional fixed angle ATR accessory and no polarizer working  with partially or completely polarizing samples can compare them with  the polarized spectra in this library.

Rp  and Rs polarized spectra offer further advantages. With polarization,  ATR makes it easy to see the isotropic vs anisotropic character of a  given sample, especially with glassy solids such as glass plating and  plastic resin slabs. Strongly anisotropic Rp and Rs spectra can differ  greatly from the corresponding nonpolarized spectra. This provides for  distinctive spectra that are useful for searching and it gives a new  level of understanding about the surface of samples. Automotive lighting  manufacturers, and others producing optics from commodity resins,  should find this especially useful.  FTIR users working in product  failure analysis, forensic trace analysis and other fields will find  these data useful and fascinating.

Each  multiangle ATR data set was run with a full background spectrum at  every angle and polarization.  Data collection was automated with motors  to select the AOI and polarization and to direct the FTIR system.

The  spectra were run on a large Zinc selenide (ZnSe) ATR prism with a  diameter of about 3/4" with a 45 degree face for the incident beam.

The library is provided with the FDM SearchFaster(tm) software.

Keywords: dielectric, chemical properties, variable angle ATR, thin film