So, therefore, mol bar, one over the wavelength, should be meters minus 1.

But you'll find in a lot of spectroscopy,

it's defined as centimeters minus 1.

Especially in new, move on to infrared spectroscopy,

you can see an infrared spectrum, it's usually defined in centimeters minus 1.

And usually, you might be wondering why, do they use different units for

different spectrosities?

Cuz sometimes it's just easier to understand, the way the region of infrared

has nice numbers, if you like, in centimeters minus 1.

So it's easy to follow variations in it, whereas,

in something like UV spectroscopy, sometimes they talk about nanometers.

Again, that's because it gives you nice numbers.

You don't want lots of exponential numbers,

cuz it's difficult to understand it.

But they, as the wave numbers v is minus 1 but new n,

you usually end up in centimeters.

And, again, sometimes students have a lot of trouble converting,

say from new meters minus 1, to centimeters minus one.

What you've got to remember here is, you have a 100 centimeters in a meter.

Most people get that, but

then it's going the other way around that people find difficult.

And you have to think of the number of ways in a given distance.

So here we have a [INAUDIBLE] per meter, so the number of waves in that

is going to be a lot bigger than a number of waves in a centimeter, per centimeter.

So, there's a 100 times more waves, if you like,

in a meter than there is in a centimeter.