On the basis of reported experimental vapor-liquid equilibrium (VLE) data of NH

3

-1-ethyl-3-methylimidazolium acetate (NH

3

-[Emim

]

Ac)

NH

3

-1-butyl-3-methylimidazolium tetrafluoroborate (NH

3

-[Bmim

]

[BF

4

]

)

NH

3

-1

3-dimethylimidazolium dimethyl phosphate (NH

3

-[Mmim

]

DMP) and NH

3

-1-ethyl-3-methylimidazolium ethylsulfate (NH

3

-[Emim

]

EtOSO

3

) binary systems

the interaction parameters of 14 new groups have been regressed by means of the UNIFAC model. To validate the reliability of the method

these parameters have been used to calculate the VLE data with the average relative deviation of pressures of less than 9.35%. The infinite dilution activity coefficient (γ

1

∞

) and the absorption potential (Ψ

1

) are important evaluation criterions of the affinity between working pair species of the absorption cycle. The UNIFAC model is implemented to predict the values of γ

1

∞

and Ψ

1

of 16 sets of NH

3

-ionic liquid (IL) systems. The work found that the Ψ

1

gradually increases following the impact order: Ψ

1

([C

n

mim

]

[BF

4

]

)Ψ

1

([C

n

mim

]

EtOSO

3

)Ψ

1

([C

n

mim

]

DMP)Ψ

1

([C

n

mim

]

Ac) (n=1

2

3

...) at a given cation of IL species and constant temperature

and Ψ

1

([Mmim

]

X)Ψ

1

([Emim

]

X)Ψ

1

([Pmim

]

X)Ψ

1

([Bmim

]

X) (X=Ac

[BF

4

]

DMP or EtOSO

3

) at a given anion of IL species and constant temperature. Furthermore

the Ψ

1

gradually increases with increasing temperature. Then

it could be concluded that the working pair NH

3

-[Bmim

]

Ac has the best potential research value relatively.