Rowland Ghosts
Definition and meaning of Rowland Ghosts in chemistry.
Rowland ghosts are false, extraneous spectral lines that appear in a spectrum due to periodic mechanical errors in the spacing of the grooves on a diffraction grating.
In more detail
When a diffraction grating is manufactured with slight, regular mechanical imperfections by a ruling engine, it acts as a secondary grating superimposed on the primary one. This periodic error causes a small fraction of the diffracted light to appear as weak, symmetrical satellite lines on either side of a strong parent spectral line. These optical artifacts can severely interfere with the quantitative analysis of trace elements by masking weak analyte signals or being misidentified as new emission lines. Modern holographic gratings avoid this issue entirely.
Key facts
| Field | Analytical Chemistry |
|---|---|
| Cause | Periodic grating errors |
| Effect | False spectral lines |
In atomic emission spectroscopy, an intense mercury emission line might be flanked by faint Rowland ghosts that an inexperienced analyst could mistakenly identify as actual trace impurities within the sample.
Frequently asked questions
How can Rowland ghosts be completely eliminated in modern spectrometers?
They can be eliminated by utilizing holographically recorded gratings, which are produced using interference patterns and do not possess the periodic mechanical errors of mechanically ruled gratings.