Emission lines from the Deuterium lamp are split into two lines

Hi everyone,

We are using a UV-VIS-NIR model Cary 5000. Recently when we validated the instrument. However, at the wavelength accuracy test using the Deuterium lamp, we found that 486 and 656.1 nm emission lines have been split into two emission lines. However, when the instrument was just brought, there were only single emission lines (486 and 656.1 nm) from the Deuterium lamp as I would like to add the photos below.

These are emission lines that we currently validated our instrument


And these are emission lines from the Deuterium lamp when the instrument was new


Now, the wavelength accuracy test of our instrument has failed, and we can not use it.

Has any experienced this problem like us and why there are also more peaks near 486 and 656.1 nm?

Could this be due to our lamp or any other parts of our instrument has failed?

I would appreciate it if you could share with us your experience and solutions to address this problem.

Thank you very much.

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