Enter a value or expression for the Molar mass Mw for each species. The default value is 0.032 kg/mol, which is the molar mass of O
2 gas.
 
    This section is available when the Migration in electric field check box is selected in the 
Transport Mechanisms section of the interface. Enter the charge number 
zw (dimensionless, but requires a plus or minus sign) for each species.