An analysis of n = 3 \to 2 transition lines of carbon-like silicon reveals that some ratios of line intensities are sensitive to the electron density .
The ratio between two group of 3 d \to 2 p transition lines at 55.246 Å and 55.346 Å is a good n _ { e } -diagnostic technique , due to its insensitivity to the electron temperature .
Using this property , a lower limit of the density of 0.6 \times 10 ^ { 8 } cm ^ { -3 } is derived for Procyon , which is consistent with that constrained by C V and Si X emissions .
Significant discrepancies in ratios of 3 s \to 2 p lines to 3 d \to 2 p lines between theoretical predictions and observed values , are found , by the spectral analysis of Procyon observed with the Chandra High Resolution Transmission Grating spectra .
The difference exceeding a factor of 3 , can not be explained by the uncertainty of atomic data .
The opacity effect is also not a choice as reported by Ness and co-workers .
For the 3 s \to 2 p line at 61.611 Å , present work indicates that the large discrepancy may be due to the contamination from a S VIII line at 61.645 Å .
For the lines at 61.702 and 61.846 Å , we suggest that the discrepancies may be attributed to contaminations of unknown lines . PACS : 95.20.Jg ; 97.10.Ex ; 95.85.Nv