To gather the emission spectrum of the laser, we used a thermocouple power gauge and a strip-chart recorder. All data was taken with a potential of 18,000 Volts across the plasma. Due to the slow response time and the thermocouple, the emission peaks are smeared into one large emission mountain. The top picture is the band corresponding to transitions from the (001) asymmetric vibrational mode to the (100) symmetric vibrational mode. The left hump is the P branch and the right hump is the R branch.
The next photo is the band corresponding to transitions from the (001) asymmetric vibrational mode to the (020) bending vibrational mode. Again, we see the P branch on the left and the R branch on the right. Although it is difficult to tell from the small photo, the separation of the peaks increases as we move farther from the band center (v0).
Notice that in both bands, the P branch has a higher intensity than the R branch. This results from a quantum mechanical effect whereby the wave functions overlap in such a way to make P branch transitions more probable than R branch transitions. According to Eastham, peaks in the first band have been observed from R(0) at 10.39 microns to R(62) at 10.02 microns as well as P(2) at 10.42 microns to P(68) at 11.18 microns. The lasing transition with maximum intensity P(22) at about 10.6 microns (Eastham 205). The following data was taken by hand-- it is the R branch of the transitions from (001) to (020). We see that R(12) is right in the center of the maximum.
The horizontal scale is the micrometer reading on the Littrow grating. Energy increases to the left. Vertical scale is Watts/cm2.
By knowing the frequency of the output at the band center (v0) and the separation between peaks, we should be able to find the moment of inertia of the CO2 molecule. We know that the separation between peaks is:
The R(0) line has a wavelength of 10.39 microns, and the R(62) line has a wavelength of 10.02 microns (Eastham 204). Using the formula
and a little algebra, we calculate that the E0 energy difference between the ground state (001) and the ground state of (100) is E0= 1.9107 *10-20 Joules, and that for the rotational inertia, we get a value of I=9.609*10-39 g-cm2 (compare to HCL, for which I=2.60*10-40 g-cm2 (Shankland 153)).