Experimental verification of the breakdown of the electric dipole rotational selection rule in electron impact ionization--excitation of N/sub 2/

Journal Article · Wed Dec 15 04:00:00 EST 1982 · J. Chem. Phys.; (United States)

OSTI ID:6573546

Hernandez, S P; Dagdigian, P J; Doering, J P

Variable energy (60--1500 eV) electron impact excitation of cold (approx.10 K) N/sub 2/ supersonic beams has been used to produce excited N/sup +//sub 2/ B /sup 2/..sigma../sup +//sub u/ ions whose rotational energy distribution has been determined by spectroscopic examination of N/sub 2//sup +/ first negative system (B /sup 2/..sigma../sup +//sub u/..-->..X /sup 2/..sigma../sup +//sub g/) emissions. For energies >800 eV, the rotational state distribution is found to be constant with electron energy. The distribution is non-Boltzmann with a peak at the N' = 1 rotational state and a long tail to higher energies. At high electron energies, the electric dipole selection rule (Vertical Bar..delta..JVertical Bar = 1) is expected to be obeyed in the ionization--excitation process. Above 800 eV, this rule is followed, and the non-Boltzmann B /sup 2/..sigma../sub u//sup +/ rotational distribution arises from the non-Boltzmann rotational distribution in the neutral supersonic N/sub 2/ beam. Below 800 eV, however, breakdown of the Vertical Bar..delta..JVertical Bar = 1 selection rule occurs with Vertical Bar..delta..JVertical Bar = 3 transitions observed first, followed by much larger ..delta..J transitions at low electron energies (<100 eV). Implications of this effect for geophysics and supersonic beam diagnostics, as well as the theoretical questions involved, are discussed.

• Research Organization: Department of Chemistry, The Johns Hopkins University, Baltimore, Maryland 21218
• OSTI ID: 6573546
• Journal Information: J. Chem. Phys.; (United States), Journal Name: J. Chem. Phys.; (United States) Vol. 77:12; ISSN JCPSA
• Country of Publication: United States
• Language: English

Related Subjects

640304* -- Atomic
Molecular &amp; Chemical Physics-- Collision Phenomena
74 ATOMIC AND MOLECULAR PHYSICS
BEAMS
COLLISIONS
ELECTRON COLLISIONS
ELECTRON-MOLECULE COLLISIONS
ELEMENTS
EMISSION SPECTRA
ENERGY LEVELS
ENERGY-LEVEL TRANSITIONS
EXCITATION
EXCITED STATES
IONIZATION
MOLECULAR BEAMS
MOLECULE COLLISIONS
NITROGEN
NONMETALS
ROTATIONAL STATES
SELECTION RULES
SPECTRA