Nitrogen difluoride


Nitrogen difluoride, also known as difluoroamino is a reactive radical molecule with formula NF2•. This small molecule is in equilibrium with its dimer dinitrogen tetrafluoride.
N2F4 2 NF2•
As the temperature increases the proportion of NF2• increases.
The molecule is unusual in that it has an odd number of electrons, yet is stable enough to study experimentally.

Properties

The energy needed to break the N-N bond in N2F4 is 20.8 kcal/mol. This compares to 14.6 kcal/mol in N2O4 and 10.2 in N2O2 and 60 kcal/mol in hydrazine N2H4.
ΔHf = 34.421 kJ/mol.
The heat of dissociation of N2F4 forming NF2 is 20 kcal/mol. Entropy change in this dissociation is 38.6 eu.
In the molecule the N–F bond length is 1.3494 Å and the angle subtended at FNF is 103.33°.
At room temperature N2F4 is mostly associated with only 0.7% in the form of NF2• at 5mm Hg pressure. When the temperature rises to 225 °C, it mostly dissociates with 99% in the form of NF2•.
In the infrared spectrum the N-F bond in NF2 has a symmetrical stretching frequency of 1075 cm−1. This compares to 1115 in NF, 1021 in NF3 and 998 in N2F4.
The microwave spectrum shows numerous lines due to spin transitions, with or without nuclear spin transitions. The lines form set of two triplets for anti-symmetric singlet, or two triplets of triplets for symmetric triplet. Lines appear around 14-15, 24, 25, 26, 27, 28-29, 33, 60, 61, 62, 65 GHz. The rotational constants for the NF2• molecule as A=70496 MHz B=11872.2 MHz C=10136.5 MHz. Inertial defect Δ=0.1204 muÅ2. The centrifugal distortion constants are τaaaa=-7.75 τbbbb=-0.081 τaabb=0.30 τabab=-0.13.
The dipole moment is 0.13 D.
The ground electronic state of the molecule is 2B1.
The gas is often contaminated with NO or N2O.

Use

Nitrogen difluoride is formed during the function of a xenon monofluoride excimer laser. Nitrogen trifluoride is the halide carrier gas, which releases fluoride ions when impacted by electrons:
NF3 + e− → NF2 + F−
The free fluoride ion goes on to react with xenon cations.
Nitrogen difluoride can be consumed further to yield nitrogen monofluoride.
NF2• + e− → NF + F−

Extra reading