The temperature dependence of Mössbauer quadrupole splitting values: a quantum chemical analysis

The two key parameters extracted from Mössbauer spectroscopy, the isomer shift and the quadrupole splitting, have well-known temperature dependencies. While the values’ increase or decrease with sample temperature have long been established, the microscopic origins are less clear. For quantum chemical calculations – formally representing the situation at 0 K – significant discrepancies with experiment can arise depending on the temperature. Herein, we introduce an enesemble-based appraoch for capturing the temperature dependence of the quadrupole splitting. Our method is exemplified with [Fe(TPP)(2-MeHIm)]. We rationalise the temperature dependence by changes in the electric field gradient due to specific vibrational distortions. We use a normal mode fitting approach to isolate the specific collective nuclear movements that are associated with the changes in the quadrupole splitting.