Accession Number:

ADA076100

Title:

The Effects of Velocity-Changing Collisions on Two-Photon and Stepwise Absorption Spectroscopic Lineshapes,

Descriptive Note:

Corporate Author:

NEW YORK UNIV N Y DEPT OF PHYSICS

Report Date:

1979-09-01

Pagination or Media Count:

23.0

Abstract:

We report the results of an experimental study of the effects of velocity-changing collisions on two-photon and stepwise absorption lineshapes. Excitation spectra for the 3S12 yields 3P12 yields 4D32 transitions of sodium atoms undergoing collisions with foreign gas perturbers are obtained. These spectra are obtained with two cw dye lasers. One laser, the pump laser, is tuned 1.6 GHz below the 3S12 yields 3P12 transition frequency and excites a nonthermal longitudinal velocity distribution of excited 3P12 atoms in vapor. Absorption of the second probe laser is used to monitor the steady state excited state distribution which is a result of collisions with rare gas atoms. The spectra are obtained for various pressures of He, Ne, and Kr gases and are fit to a theoretical model which utilizes either the phenomenological Keilson-Stoerer or the classical hard sphere collision kernel. The theoretical model includes the effects of collisionally aided excitation of the 3P12 state as well as effects due to fine-structure state-changing collisions. Although both kernels are found to predict lineshapes which are in reasonable agreement with the experimental results, the hard sphere kernel is found superior as it gives a better description of the effects of large angle scattering for heavy perturbers. Neither kernel provides a fully adequate description over the entire line profile. The experimental data is used to extract effective hard-sphere collision cross sections for collisions between sodium 3P12 atoms and helium, neon and krypton perturbers. Author

Subject Categories:

  • Atomic and Molecular Physics and Spectroscopy

Distribution Statement:

APPROVED FOR PUBLIC RELEASE