Using

Display Resolution

The displayed data is limited to 10,000 points. As the X-axis limits are reduced, the App recalculates the necessary display resolution. This reduction does not impact the saved data. The X-axis display reduction is given under the SPECTRUM STATISTICS section and is updated as the x-axis limits are changed. The user may override this feature and display all data points, but at the risk of substantially slowing down the App.

Spectral Sources

  • Sharpe S.W., T.J. Johnson, R.L. Sams, P.M. Chu, G.C. Rhoderick, and P.A. Johnson. 2004. “Gas-Phase Database for Quantitative Infrared Spectroscopy”, Applied Spectroscopy, 58, no. 12, pages 1452-1461.
  • Timothy J. Johnson, Luisa T.M. Profeta, Robert L. Sams, David W.T. Griffith, Robert L. Yokelson, “An Infrared Spectral Database for Detection of Gases Emitted by Biomass Burning”, Vibrational Spectroscopy, Volume 53, Issue 1, 2010, Pages 97-102.

Spectral selection

Spectra are selected by one of two methods: (1) A pull down list based on common chemical names. Be aware that many chemicals have multiple names. For instance, water can also be correctly called “dihydrogen oxide”. (2) An entry field based on the Chemical Abstract Service (CAS) number. The CAS number is a unique identifier for each chemical. CAS numbers can be up to 10 digits, separated by two hyphens, where the last digit is a checksum. For example, water is given the CAS number 7732-18-5.

X-Axis

The X-axis can be expressed as wavenumbers (cm-1) or wavelength (microns). The X-axis may be reversed (high to low) by selecting the “Reverse” check-box. The X-axis limits may be updated by (1) entering new values via the keyboard, or (2) placing the cursor over the spectrum and tapping once or twice. One tap will update the low limit and two taps will update the high limit. To reset the X-axis to full spectral region, hit the reset button or type command-r.

Y-Axis (absorbance or transmittance)

  • Absorbance is a dimensionless value based on the decadic (base-10) log of I/Io and depends on concentration and path length. Absorbance can also be calculated using the Naperian or base-e logarithm. To convert from decadic to Naperian absorbance, multiply the decadic absorbance value by 2.302585.
  • Transmittance is dimensionless, represents the percent of light that passes through a sample, and depends on concentration and path length.

When in absorbance mode, the area under the absorbance spectrum is displayed as well as the integrated cross-section (cm*molecule-1).

Convolving or de-resolving spectra

Spectra can be convolved using a Gaussian profile, with full-width-half-maximum (FWHM) values between 0.5 and 15 cm-1. This is equivalent to de-resolving the spectral data. The convolution algorithm requires that the first and last (approximately) 60 cm-1 values be destroyed.

Saving spectra

Save options are available under the File menu. Each spectrum is saved along with a metadata header containing information regarding the spectrum. Spectra are saved in comma-separated, txt, two-column format. The user can save the entire spectrum or spectrum constrained by the X-axis limits.