Award Date


Degree Type


Degree Name

Doctor of Philosophy (PhD)



Number of Pages



The visible {dollar}A\sp2\Pi\sb{u} \gets X\sp2\Sigma\sbsp{g}{+}{dollar} absorption spectrum of N{dollar}\sb2\sp+{dollar} was observed by using a coaxial ion beam laser beam technique for the first time. The resonances are detected by allowing the ion beam to collide with buffer gas and detecting the surviving ion beam current. Because the collisional cross-section depends on the internal state of the ion, the surviving ion beam current changes when the laser frequency is resonant with the ions. This technique can detect a fractional change in collisional cross section of only 0.03% from one quantum state to another. The fractional noise in ion current {dollar}\Delta I/I{dollar} is a few parts in {dollar}10\sp{-7}{dollar} (3 second average time) is consistent with the shot noise limit. The frequency resolution {dollar}\Delta\nu/\nu{dollar} in this experiment is {dollar}2 \times 10\sp{-7}.{dollar} Compared to the commonly used technique of absorption spectroscopy in a discharge, the Doppler width in this experiment is reduced by a factor of 10-20. A number of previously unresolved lower rotational doublet lines in the {dollar}A\sp2\Pi\sb{u} \gets X\sp2\Sigma\sbsp{g}{+}{dollar} (4, 0) band are fully resolved and the energy splittings are measured for the first time in this experiment. The spin-rotation coupling constant of N{dollar}\sb2\sp+{dollar} in the {dollar}X\sp2\Sigma\sbsp{g}{+}{dollar} (v = 0) state is obtained by the direct measurement of the fully resolved doublets whose splitting is caused by the interaction between the electron spin with the molecular rotation. The technique demonstrated here is applicable to a wide variety of molecular ions.


Beam; Coaxial; Coaxial Ion Beam Laser; High; Ion; Laser; Nitrogen; Resolution; Spectroscopy; Coaxial Ion Beam Laser; Nitrogen

Controlled Subject

Molecular dynamics

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3573.76 KB

Degree Grantor

University of Nevada, Las Vegas




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