CHClF2 Vibrational Modes

Characteristic Vibrations of CHClF₂

(C_s symmetry)

CHClF₂ (chlorodifluoromethane, also known as HCFC-22 or Freon-22) is roughly tetrahedral, like the other halogen-substituted methanes (e.g., CFC-11, CFC-13). There are no significant natural sources of this molecule, and it is as a result of human activity that the present atmosphere contains ~0.132 ppb of CHClF₂. CHClF₂ has been used as a more ozone-friendly substitute for CFC's in refrigeration, and as a propellant. HCFC's like CHClF₂ break down relative quickly in the atmosphere (with a lifetime of roughly 10 years), and so will not accumulate in the stratosphere as easily as the more durable CFC's, which last 50-100 years. However, CHClF₂ does have significant ozone-destroying potential, and production will eventually be scaled back. CHClF₂ is a slight contributor to the human-induced strengthening of Earth's greenhouse effect, adding a radiative forcing ≈ 0.03 Watts/m² (IPCC).
Since both stable isotopes of chlorine are common (³⁵Cl - 75.77%, ³⁷Cl - 24.23%), atmospheric CHClF₂ is a mixture of ¹²C¹H³⁵Cl¹⁹F₂ (~75%) and ¹²C¹H³⁷Cl¹⁹F₂ (~24%). Both isotopic forms of the molecule have C_s point-group symmetry. All nine characteristic vibrational modes can interact with infrared light, scattering or absorbing heat radiation from the Earth before it escapes to space. The normal modes depicted below were modeled using hybrid density functional theory (B3LYP) and the cc-pVTZ basis set. Vibrational frequencies, tabulated by Snels and D'Amico (2001, J. Mol. Spectrosc. 209:1-10), are also shown -- values for the ¹²C¹H³⁵Cl¹⁹F₂, isotopologue are listed first, with values for ¹²C¹H³⁷Cl¹⁹F₂ underneath. These are the fundamental frequencies, and have not been corrected for anharmonicity.

ν₁ = 3021.6 cm^-1(³⁵Cl) 3021.4 cm^-1 (³⁷Cl)A' Symmetry	ν₂ = 1313.2 cm^-1(³⁵Cl) N/A cm^-1 (³⁷Cl)A' Symmetry	ν₃ = 1108.7 cm^-1(³⁵Cl) 1108.7 cm^-1 (³⁷Cl)A' Symmetry

ν₄ = 809.7 cm^-1(³⁵Cl) 804.5 cm^-1 (³⁷Cl)A' Symmetry	ν₅ = 596.4 cm^-1(³⁵Cl) 595.4 cm^-1 (³⁷Cl)A' Symmetry	ν₆ = 412.9 cm^-1(³⁵Cl) 407.9 cm^-1 (³⁷Cl)A' Symmetry

ν₇ = 1351.3 cm^-1(³⁵Cl) N/A cm^-1 (³⁷Cl)A'' Symmetry	ν₈ = 1127.3 cm^-1(³⁵Cl) 1127.1 cm^-1 (³⁷Cl)A'' Symmetry	ν₉ = 366.2 cm^-1(³⁵Cl) 364.3 cm^-1 (³⁷Cl)A'' Symmetry