ABSTRACT: In this lab we calculated the vibrational constants and Morse parameters of the diatomic iodine molecule by examining the spectrum emitted by argon-ion-laser-pumped iodine vapor. We found the Morse parameters to be De = ne2 (4nexe)-1 cm-1 and b = (2p2cm(Deh)-1)1/2ne cm-1. These values differ from the accepted values of De and b by 28% and 18%, respectively. INTRODUCTION: An examination of the vibrational spectra of the diatomic iodine molecule can, through several measurements and calculations, yield the molecules Morse parameters. This is accomplished by examining the spacing of the peaks of the wavelengths fluoresced by iodine vapor that has been excited through laser pumping, from which the vibrational constants and therefore the Morse parameters can be calculated. THEORY: A diatomic molecule such as I2 can have many different potential energies due to the varying energy levels created by the interplay between magnetic and strong forces as the interatomic separation of the molecule varies. Therefore, when an electron in the molecule is excited to a higher energy band, many energy gaps of different distances exist for the electron to drop down. Each transition has a particular wavelength of light associated with it. By examining the spacing between these wavelengths vibrational constants can be determined, through the following method: For a harmonic oscillator E=hf(v+1/2), so for an enharmonic oscillator we can take the first two terms of a Taylor series expansion; ne(v+1/2)- nexe(v+1/2)2. Thus wave number of a photon transitioning from vibrational level v to vibrational level v has wave number equal to the difference of energies: n(v, v) = nel + ne(v+1/2) - nexe(v+1/2)2 - ne(v+1/2) + nexe(v+1/2)2 Equation 1 The spacings of wavelength peaks represent the difference between two adjacent transitions, so the difference of photon energies W(v) can be written: W(v) = n(v, v) - n(v, v+1) Equation 2 Which, through algebraic calculations that can be found in Appendix A, becomes the equation: W(v) = (ne  2xene)  (2xene)v Equation 3 The equation describes the linear relation between W and v. Thus by graphing this data the vibrational constants xe and ne can be determined. From these, the Morse parameters of the diatomic molecule can be calculated as follows: De = ne2 (4nexe)-1 b = (2p2cm(Deh)-1)1/2ne Equation 4 Equation 5 PROCEDURE: In this lab we used the 514.5 nm output of an argon-ion laser to pump iodine vapor contained in a glass chamber from vibrational energy level 0 to vibrational energy level 43. A PC-mounted spectrometer collected wavelength and intensity data from the fluorescing iodine vapor. This data was compiled in a spreadsheet for examination of wavelength peak separation, from which the vibrational constants and Morse parameters were calculated. RESULTS: The wavelength and intensity data we collected can be found in Appendix B. The peaks were identified and converted to wave number in Appendix C, from which values for W are calculated. Appendix D contains the graph of W vs. v from which we determined the vibrational constants. We found the vibrational constants to be xe = 0.0031 ne = 214.45 These correspond to Morse parameters De = 17421.35 cm-1 b = 1.576 x 108 cm-1 Our value for De is off of the accepted value of 12410 by 28%, while our value for b is off of the accepted value of 1.858 x 108 by 18%. CONCLUSION: That our calculated values landed within 28% and 18% of the accepted values shows that our experimental methods and calculations are sound. However, improvement on the quality of our Morse parameters could be achieved by collecting better data. A better alignment of the fiber optic cable with the beam of fluorescing iodine would yield truer peaks which would reduce the uncertainty in peak spacing. This would result in a more accurate, straighter graph from which to calculate vibrational constants and Morse parameters.