Anharmonic effects in spectroscopy
When calculating an infrared spectrum from quantum chemistry methods, such as density functional theory, a core assumption is the harmonic approximation. Although such an approximation leads in certain cases to a good agreement with experimental results, it can also fail when describing an infrared spectrum. To remedy this problem, many quantum chemistry software packages allow the computation of “anharmonic effects”, but only for what is known as 2-quanta modes. Researchers at FELIX have shown, by combining gas-phase infrared spectroscopy measurements of the molecule phenylacetylene (recently detected in space), that 2-quanta modes are still an oversimplification of the complex energy surface of carbon-based molecules. Researchers at FELIX have shown, by combining gas-phase infrared spectroscopy measurements of the molecule phenylacetylene (recently detected in space), that 2-quanta modes are still an oversimplification of the complex energy surface of carbon-based molecules.
