Knowledge Bank

The electron spectrometer described elsewhere1 has been used in a study of the excitation of the $X1\Sigma +(\nu \prime \prime =o)\to A1\Pi (\nu \prime =\nu )$ transition in carbon monoxide by electron impact. Other work in this laboratory2,3 has already shown the close connection between excitation by radiation absorption and by electron impact. Resolution of the electron spectrometer is insufficient, in this case, to separate excitations to different vibrational levels. The envelope shape can, however, be compared with theoretical calculations when account is taken of energy spread in the electron beam and the finite resolution of the velocity analyzer. The envelope shape was determined experimentally by averaging six electron impact energy spectra taken at scattering angles from 3.4 to 8.4 degrees with an incident electron energy of 508 volts. In accord with theoretical predictions this envelope shape was independent of scattering angle. The energy distribution at the exit slit of the analyzer was obtained from measurements on helium. The theoretical calculations are based on harmonic oscillator wave functions in the ground and excited states. The theoretical results of Hutchisson4 have been used to calculate the relative transition probabilities. These transition moments are the same as are encountered in the theory of radiation absorption. Theoretical intensity distributions are in excellent agreement with experiment up to $\nu \prime =4$. At the higher levels the agreement becomes increasingly poorer, probably due to anharmonicity.