OK chem-wizards...(adsbygoogle = window.adsbygoogle || []).push({});

I'm looking at a paper which states

"....the integrated absorptivity of the stretching vibrations of a water molecule is 4.89 cm micro mol^-1"

(I'm transcribing a 'mu' character as micro in the above. If mu doesn't stand for micro, then let me know!)

OK, so some questions:

1) Is the paper quoting an integrated 'molar absorptivity'?

2) The integration is over the frequency axis, but is this frequency in wave-numbers?

3) Is this defn. for molar absorptivity correct?

Molar Absorptivity,? = A/ c l

( where A= absorbance, c = sample concentration in moles/liter

& l = length of light path through the cuvette in cm.)

taken from http://www.cem.msu.edu/~reusch/VirtualText/Spectrpy/UV-Vis/uvspec.htm

4) According to this Wikipedia article, absorbance is calculated as a base 10 logarithm of I/I0. Is that defn. universally used?

http://en.wikipedia.org/wiki/Absorbance

5) I can't understand the units. If A=absorption and alpha = absorption coefficient and L=sample length, then A=alpha L, so that means that alpha is in units of inverse length.

If e=absorptivity, and c is the concentration in mols per liter and e=A/cL=alpha/c, then e is in units of mols^-1 liters ^-1 cm^-1. Thus, I'd expect the integrated absorptivity to be in mols^-1 liters^ -1 cm ^-2, given that the integral is over wavenumbers which have units of cm^-1.

6) Basically what I want is to convert the number in the paper into a value for the absorption coefficient.

Thanks in advance for any help!

**Physics Forums - The Fusion of Science and Community**

Dismiss Notice

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Explain molar absorptivity to a dumb physicist.

Loading...

Similar Threads for Explain molar absorptivity | Date |
---|---|

A Is there anyone who can explain Strukturbericht symbol? | Dec 12, 2016 |

Can someone explain peierls distortion/transition to me? | Nov 13, 2015 |

Explaining Band theory and Momentum Space to laymen? | Mar 22, 2015 |

Can we explain shielding effect using electric field ? | Jan 7, 2015 |

Molar Mass of Graphene and its strength | Oct 20, 2010 |

**Physics Forums - The Fusion of Science and Community**