Characteristic Vibrations of CCl2F2

(C2v or Cs symmetry)

CCl2F2 (dichlorodifluoromethane, also known as CFC-12 or Freon-12) is an approximately tetrahedral molecule. It does not occur naturally, and the current atmospheric abundance of ~0.533 ppb is the result of human-induced emissions. Until recently, CCl2F2 was extensively used for refrigeration, and as a propellant in aerosol sprays, favored because of its favorable thermal properties and chemical inertness. Unfortunately, this chemical inertness led to accumulation in the atmosphere, where its breakdown product Cl• promotes stratospheric decomposition of ozone. Manufacture of CCl2F2 was phased out during the 1990's to preserve the Earth's protective ozone layer. CCl2F2 is also a minor contributor to the Earth's enhanced greenhouse effect, adding a radiative forcing ≈ 0.17 Watts/m2 (IPCC).
Since both stable isotopes of chlorine are common (35Cl - 75.77%, 37Cl - 24.23%), some atmospheric CCl2F2 occurs as an asymmetric isotopologue (12C37Cl35Cl19F2, ~36%) with Cs point-group symmetry, mixed in with the symmetric (C2v) isotopologues (12C35Cl219F2, ~57%; 12C37Cl219F2, ~6%). Both symmetric and asymmetric molecules have eight vibrational modes that interact strongly with infrared light (o1 - o4, o6 - o9) and these modes are the most likely to absorb or scatter infrared heat radiation from the Earth before it can escape to space. o5 is also slightly infrared-active in the asymmetric molecules   The normal modes depicted below were modeled using hybrid density functional theory (B3LYP) and the cc-pVTZ basis set. Vibrational frequencies tabulated by D'Amico et al. (2002, Phys. Chem. Chem. Phys. 4:1531-1536) are also shown -- values for the 12C35Cl219F2, isotopologue are listed first, with values for 12C37Cl35Cl19F2 underneath. Symmetry species are shown for 12C35Cl219F2. Listed frequencies have not been corrected for anharmonicity.

o1 = 1101.4 cm-1 (sym.)
N/A (asym.)
A1 Symmetry

o2 = 666.8 cm-1 (sym.)
665.5 cm-1 (asym.)
A1 Symmetry

o3 = 468.5 cm-1 (sym.)
N/A cm-1 (asym.)
A1 Symmetr
CCl2F2_nu1 CCl2F2_nu3 CCl2F2_nu4

o4 = 261.6 cm-1 (sym.)
259.1 cm-1 (asym.)
A1 Symmetry

o5 = 320.7 cm-1 (sym.)
319.5 cm-1 (asym.)
A2 Symmetry

o6 = 923.2 cm-1 (sym.)
921.8 cm-1 (asym.)
B1 Symmetry
CCl2F2_nu6 CCl2F2_nu9 CCl2F2_nu2

o7 = 437.0 cm-1 (sym.)
433.5 cm-1 (asym.)
B1 Symmetry

o8 = 1161.1 cm-1 (sym.)
1161.0 cm-1 (asym.)
B2 Symmetry

o9 = 461.8 cm-1 (sym.)
460.6 cm-1 (asym.)
B2 Symmetry
CCl2F2_nu5 CCl2F2_nu7 CCl2F2_nu8

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