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How to
convert cm-1 to microns or
nanometers
Basics
Spectroscopists
of the chemistry variety have found
that inverse cm is a wonderful way to
measure light. It is proportional to
the wavenumber and the frequency, but
it makes those of us that are trained
in rational units pull our hair out. IF
you are talking about ABSOLUTE
wavelength (i.e. the wavelength of
CO2 laser is 10.6 microns)
then the conversion goes as
follows:
Wavelength in µm =
10,000/cm-1
So
300 cm-1 => 33 microns
Wavelength in nm =
10,000,000/cm-1
so
20,000
cm-1
=> 500 nm
How to
convert microns or nm to
cm-1(inverse
cm)
Wavenumbers in
cm-1=
10,000/µm So 10.6
microns => 943
cm-1
Wavenumbers in
cm-1=
10,000,000/nm
So 632.8
nm => 15800
cm-1
How to
convert delta microns or nanometers to
delta cm-1(inverse
cm)
Of
course this is where it gets tricky,
because the result depends on the
absolute wavenumber, in other words 10
cm-1 is 1000 microns at one
wavelength, but 0.1 microns at another.
If you have a peak width of inverse
centimeters converting to a peak width
of microns could be painful. But taking
the derivative of the above equations
you can get the formula
d(Wavelength in µm) =
(10,000 * d(cm-1)/(cm-1)2)
The
notation is a little awkward, sorry.
What this means is that you take the
peak width [d(cm-1)], divide
it by the absolute wavenumber of the
center of the peak [(cm-1)]
and multiply it by 10,000 to get the
peak width in µm.
So a
peak that is centered at 943
cm-1 and is 12
cm-1 wide would be also a
peak centered at 10.6 microns and 0.13
microns wide.
d(Wavelength in nm) =
(10,000,000 * d(cm-1)/(cm-1)2)
So
a peak that is centered at 20492 cm-1
with a linewidth of 10 cm-1 would also
be a peak centered at 488 nm with a
linewidth of 2.4 ·
10-8 nm.
How to
convert delta cm-1 to delta
micrometers or delta
nanometers
d(Wavenumber in
cm-1) = (10,000 * d(µm)/(µm)2)
Or
a peak that has wavelength of 33
microns and is 0.2 microns wide would
be centered at 303 cm-1 and
be 1.84 cm-1 wide
d(Wavenumber in
cm-1) = (10,000,000 *
d(nm)/(nm)2)
or a peak that has a
wavelength of 1.06 nm and a linewidth
of .01 nm would be centered at 9433962
cm-1 with a line width of
89000 cm-1 |
