[soaring206]

Okay, I'm trying to do a problem involving Heisenberg's uncertainty principle (?x * ?p_x ? ?/2), and I know what the answer is, but I can't figure out how to get the answer from what's been given to me.  This is the problem:

Though not strictly equivalent, there is a similar uncertainty relationship between the observables time and energy:

?E * ?t ? ?/2

In emission spectroscopy, the width of the lines (which gives a measure of ?E) in a spectrum can be related to the lifetime (that is, ?t) of the excited state.  If the width of a spectral line of a certain electronic transition is 1.00 cm^-1, what is the minimum uncertainty in the lifetime of the transition?

Now, I know that ? = h/2?, and if the equation is rearranged to solve for ?t, it becomes ?t ? h/4??E (where h = Planck's constant (6.626x10^-34 J*s)), but when I plug in all my numbers (6.626x10^-34 J*s/4*3.14*1.00 cm^-1), the units don't work out to give me seconds for ?t, and I don't come up with the book's answer of ?t ? 2.65x10^-12 s.  Could someone please point me in the right direction with this?  Thank you!

[Mitch]

You need to convert 1.00cm-1 to units of Joules.

[soaring206]

Ah ha...it's always the dumb little things that get me.  Thank you very much!