WinPlotr, which is can be downloaded at www.ccp14.ac.uk, can do wavelength conversion. Read in your data and choose 'Change wavelength' in the 'X space ' menu. The converted data will be plotted along with your original data. To save the converted data to a file, choose 'save data as multicolumn file' from the 'File' menu. The data will not be saved with constant step length, but this can be achieved by interpolation in e.g. Origin or Excel.
The simplest thing to do if you just want to visually compare two data sets at different wavelenghts, is to open them both in WinPlotr and plot them in e.g. Q-space (use the 'X-space' menu again). Regards, Magnus H. Sorby
