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Fourier transform infrared spectroscopy (FTIR) [1] is a technique used to obtain an infrared spectrum of absorption or emission of a solid, liquid, or gas. An FTIR spectrometer simultaneously collects high-resolution spectral data over a wide spectral range.
An "interferogram" from a Fourier-transform spectrometer. This is the "raw data" which can be Fourier-transformed into an actual spectrum. The peak at the center is the ZPD position ("zero path difference"): Here, all the light passes through the interferometer because its two arms have equal length.
The spectra are plotted in units of log inverse reflectance (log 1/R) versus wavenumber. Alternative plots of Kubelka-Munk units can be used, which relate reflectance to concentration using a scaling factor. A reflectance standard is needed in order to quantify the reflectance of the sample because it cannot be determined directly. [2] [3]
By carefully interpreting the signs of the 2D synchronous and asynchronous cross peaks with the following rules, the sequence of spectral events during the experiment can be determined: if the intensities of the bands at x and y in the dataset are changing in the same direction, the synchronous 2D cross peak at ( x , y ) is positive
Furthermore, the mean square difference between a model and the data can be calculated by adding in quadrature the bias and the standard deviation of the errors. The code for these "modified" Taylor diagrams was developed, and is available in, Python [13].
There are two main approaches to two-dimensional spectroscopy, the Fourier-transform method, in which the data is collected in the time-domain and then Fourier-transformed to obtain a frequency-frequency 2D correlation spectrum, and the frequency domain approach in which all the data is collected directly in the frequency domain.
In spectroscopy half the width at half maximum (here γ), HWHM, is in common use.For example, a Lorentzian/Cauchy distribution of height 1 / πγ can be defined by = [+ ()] =.
The program seeks to find mechanisms and their rates for all fragmentation types (EI, Tandem positive and negative mode) and correlates mass spectral peaks to a probable origin structure. It contains an isotope calculator and other features and on-line help. This program is a companion to the NIST Spectra Search Program, v.3.0.