Can Molar Absorptivity Values Be Calculated Without Experimentation?

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Discussion Overview

The discussion revolves around the possibility of calculating molar absorptivity values for various substances without experimental data. It touches on theoretical approaches, the complexity of molar absorptivity, and the need for experimental standards, as well as inquiries into related topics such as microwave spectra and temperature effects.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Homework-related

Main Points Raised

  • One participant questions whether molar absorptivity values can be calculated without experimentation.
  • Another participant asserts that accurate molar absorptivity values require experimentation with standards, citing the complexity of factors involved.
  • A request for resources on microwave spectra of specific compounds is made, indicating a need for data to support calculations.
  • Links to various resources and papers are provided, although some are noted to have limited data.
  • A participant expresses the need to calculate microwave spectra at high temperatures and references the rigid rotor model for rotational energy.
  • Discussion includes the suggestion to consider microwave emission spectra, particularly at elevated temperatures, where emission may dominate.
  • A question is raised about the relationship between emission and Blackbody Radiation.

Areas of Agreement / Disagreement

Participants generally agree that experimentation is crucial for determining molar absorptivity values, but there is no consensus on the feasibility of theoretical calculations. Multiple views on the need for experimental data and theoretical approaches remain present.

Contextual Notes

The discussion highlights limitations in the availability of comprehensive theoretical methods for calculating molar absorptivity and the dependence on specific conditions and standards for accurate analysis.

Who May Find This Useful

Researchers and students interested in spectroscopy, physical chemistry, and those working with high-temperature systems may find this discussion relevant.

sid_galt
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Is there a way of calculating molar absorptivity values of various substances without resorting to experimentation?
 
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To ascertain a molar absorptivity under certain conditions (for accurate quantitative analysis) you'll need to do some experimentation with standards, that is don't ever assume a molar absorptivity value for quantitative analysis. Molar absorptivity is pretty complex and involves many factors (e.g. orientation of the chromophore and quantum characteristics), I'm not aware of any current measures for an all around method for theoretical molar absorptivity calculations (that is for any substance). Although I suppose it's possible for compounds of a limited complexity, especially for atomic values.
 
Thank you for the reply.

Any place (books, websites) where I can find data on the microwave spectra of compounds like water, hydrogen peroxide, carbon monoxide, hydroxide ion, etc.
 
Last edited:
Thank you for the reply. The problem is that I will probably need a way to calculate the microwave spectra of the various species as I am working with multiple temperatures from 500K to 2000K.

I have found the rigid rotor model for rotational energy. Is there a way to relate the energy of the system with the temperature?
 
Perhaps then one should look for microwave emission spectrum.

I think the paper (RAdiScienceCol.pdf) goes into some detail, but I only browsed it.

At the temperatures, particularly 2000K, it would seem emission is the main effect.

I found this - http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JPCRBU000007000001000311000001&idtype=cvips&gifs=yes
but it must be purchased, and it is not clear from the abstract if it includes the temperature range of interest.

If found this string - "Microwave Spectra of Molecules of Astrophysical Interest" about midway down the NIST page - http://srdata.nist.gov/gateway/gateway?keyword=spectrum
That led me to the article above.

Perhaps you could contact the various authors.
 
Last edited by a moderator:
Emission would occur due to Blackbody Radiation right?
 

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