The key for MARVEL is to find all papers with spectroscopic data – these are the long tables usually with J at the top that we ignored for the DC project
Once you have found all the papers, you use digitisation software to convert the pdf into csv or similar files
Then you convert the original format of the table into a standardised MARVEL format
Then you put the transition data with uncertainties into MARVEL and MARVEL will give you the energies with uncertainties.
Stages of a MARVEL Project
Research Molecule
Perform a thorough literature review of molecule, identifying ideally all sources of assigned experimental transitions
Digitise the data (i.e. convert from PDF to Excel format)
Check the patterns in your transition data; e.g. for a particular branch (e.g. same initial and final electronic state, vibrational state and P/Q/R), the transition frequency should vary smoothly with the J" quantum number. You can check this by using colour-coding in Excel or graphing J vs Transition Frequency in Excel. If the data isn't smooth, there is likely digitisation errors that you need to correct. It is much easier to correct at this stage than waiting until later.
Convert transition data into MARVEL input format.
Use MARVEL to convert transition data to energy levels. This will usually be a very involved process; expect a lot of error messages. MARVEL will now update your input uncertainties in two ways:
For transitions where ratio of recommended uncertainty to initial uncertainty is below your input "Threshold for change", MARVEL will change the uncertainties automatically in the new "transitions" file.
For transitions where ratio of recommended uncertainty to initial uncertainty is above the input "Threshold of delete", MARVEL will automatically put a negative sign in front of the transition in the new "transitions" file so it is ignored in the new calculation.
I would recommend setting "Threshold for change" and "Threshold of delete" both to 3.
Once MARVEL gives you the energy levels and a "green" message: "Database is self-consistent. It does not contain any bad line!", celebrate, then
Plot Energy Level vs. J for each set of levels (i.e. all your other quantum numbers - for diatomics, this is each value of electronic state and vibrational state). These will form part of your results.
Plot Energy Level vs. J*(J+1) and fit this plot using a linear trendline. The gradient gives you the rotational constant B. You can compare this to the value in the original paper.
If either of these plots are not smooth curves, please inform your tutor, as it is likely there is an error somewhere in your input transitions.
Another Set of Instructions
Literature Search
Isolate experimental papers with wavelengths and molecular constants
Transcribe this data into spreadsheets with the aid of OCR tools.
Format into MARVEL format
MARVEL: start with Sigma+ --> Sigma+ transitions (naively should be easiest)
Low N, J and build up
Compare MARVEL energies with term values from experimental papers