It is rare to observe isomer shift around zero in the Mossbauer spectrum, however for the configurations high-spin Fe(II) S=2, intermediate-spin Fe(IV) S=1, and low-spin Fe(II) S= 0, configurations is possible (see Greenwood, N.N., Gibb, T.C.: Mössbauer Spectroscopy. Chapman and Hall, London (1971)).

Jose Humberto Araujo Dear Prof. Jose,

Thanks for your feedback. Another question I need your help is that, should I do calibration each time, before I measure a new sample? Or alpha-Fe calibration at different velocity makes any difference? I am looking forward to your reply.

Yes, for each speed it is recommended to carry out a new calibration.

Jose Humberto Araujo Dear Prof. Jose,

Is it normal that the IS is negative in a Mossbauer data? Thank you for your education in advance.

It is perfectly normal to have a negative value in the Mossbauer spectrum for low spin, Fe(II) S=0 and Fe(III) S=1/2 . (see U Gonser: Mössbauer Spectroscopy. Springer (1975) page 68.)