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!