Useful Stuff

Absorbance is calculated by taking the logarithmic ratio of the transmittance and is unitless. Consequently, one must define what base the logarithmic operation is performed in: “base-e” or base-10”. The former is know as the “natural” or “Naperian” logarithm (ln) while the latter is referred to as decadic logarithm (log). Transmittance is defined as follows:

Transmittance = T = I/I₀,

where I and I₀ correspond to the incident radiation after and before passing through the sample, respectively. Absorbance is defined as follows:

Absorbance = A = -log₁₀(T)

or

Absorbance = A = -ln(T)

Note that all IRVaporWare Absorbance data was calculated in “base-10” and needs to be multiplied by ln(10) to convert to naperian units.

Conversion between Absorbance to other common units are as follows:

To convert to units of	Multiply IRVaporWare data by
mole μmole-1 m-1	1
torr-1 cm-1	13.15789
atm-1 m-1	106
cm2 molecule-1	4.03328×10-16

To convert to units of	Multiply IRVaporWare data by
mole μmole-1 m-1	2.30259
torr-1 cm-1	30.29716
atm-1 m-1	2.30259×106
cm2 molecule-1	9.28697×10-16