Physical Chemistry 331 Quiz #9: Absorption Spectroscopy Solutions - Prof. Stefan Franzen, Quizzes of Physical Chemistry

Download Physical Chemistry 331 Quiz #9: Absorption Spectroscopy Solutions - Prof. Stefan Franzen and more Quizzes Physical Chemistry in PDF only on Docsity! 1 North Carolina State University Physical Chemistry 331 Quiz #9 Name ___________________________ Section ______ Tu/Th, Nov. 9/11, 2003 1. What is the wavenumber ν~ of an absorption maximum of λmax = 450 nm? Solution: ν~ (cm-1) = 107/ λmax (nm) = 107/ 450 = 22,222 cm-1. 2. The absorption band is approximately Gaussian in shape and has a width of 500 cm-1 and shown in Figure 1. Assuming that the band is broadened according to the time- energy uncertainty principle calculate the lifetime of the excited state. Solution: ∆t∆E = ∆t hc∆ν~ = h/4π . ∆t = 1/4π c∆ν~ = 1/4/3.141/2.99 x 1010 cm/s / 500 cm-1. = 5 x 10-15 s = 5 femtoseconds. 3. Determine the wavelength necessary to ionize a hydrogen atom (IE = 13.6 eV) Solution: 1 eV = 8065.5 cm-1 so 13.6 eV = 109690 cm-1. λmax (nm) = 107/ ν~ (cm-1) = 107/ 109690 cm-1 = 91 nm.