# Calculation of absorptivity

1. Dec 13, 2005

### sid_galt

Is there a way of calculating molar absorptivity values of various substances without resorting to experimentation?

2. Dec 13, 2005

### GCT

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.

3. Dec 13, 2005

### sid_galt

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: Dec 13, 2005
4. Dec 14, 2005

### Staff: Mentor

5. Dec 14, 2005

### sid_galt

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?

6. Dec 14, 2005

### Staff: Mentor

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/ser...00007000001000311000001&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.

7. Dec 26, 2005

### sid_galt

Emission would occur due to Blackbody Radiation right?