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Estimation of temperature

The temperature of the ion beam can be estimated through comparison of the spectroscopic lines of O2+. The following assumptions were made to quantify the jet source temperatures:

A redistribution of rotational populations results in an increase for low lying rotational states and a corresponding decrease in high lying states. Assuming that the temperature of the conventional ion source and jet source can be modelled by a Boltzmann distribution, it can be shown that the intensity of a given transition to N $^{\prime \prime }$ can be estimated from [113]:


\begin{displaymath}
I_{N',N''}~\alpha~~ S_{N',N''} exp\left(\frac{-B^{\prime\prime}}{kT}(N''(N''+1)\right)
\end{displaymath} (4.4)

Where ${\rm I_{N',N''}}$ is the intensity of a transition,   ${\rm S_{N',N''}}$ is the Honl-London factor for that transition, N $^{\prime \prime }$ is the total angular momentum excluding nuclear spin, T is the temperature and k is the Boltzmann constant.

For this work, a spectrum was recorded in the normal ion source and the intensity ratio of two lines in the same spin states was determined. The same spectrum was then recorded at a lower temperature, and the ratio of the two lines again taken, the ratio of the ratios of the intensities are used to determine a temperature for the cooler spectrum, assuming that the temperature of an EI source is 500 K. As the ratio of the two Honl-London factors remains constant with temperature, this assumption is valid.

Over 50 scans were recorded, using different source conditions and the following subsections outline these different series of experiments used to characterise and optimise the jet source.

Figure: O2+  spectrum using Jet source. Labelled transitions taken from study of Cosby et al. [125]. Laser mode hops are indicated by *
\resizebox{5in}{!}{\includegraphics{figures/o2s1612f.epsi}}




next up previous contents
Next: Nozzle Diameters Up: Results Previous: Jet apparatus results   Contents
Tim Gibbon
1999-09-06