The correct answer is: A. UV absorption spectroscopy
UV absorption spectroscopy is a technique that can be used to determine the energy difference between the initial and final states of a molecule. This is because when a molecule absorbs a photon of UV light, it is excited to a higher energy state. The energy of the photon is equal to the difference in energy between the initial and final states of the molecule.
UV absorption spectroscopy is a very sensitive technique and can be used to detect very small amounts of molecules. It is also a very versatile technique and can be used to study a wide variety of molecules.
B. UV photoelectron spectroscopy is a technique that can be used to determine the energy levels of electrons in a molecule. This is because when an electron is ejected from a molecule by a photon of UV light, the energy of the photon is equal to the energy of the electron in the molecule.
C. Infrared absorption spectroscopy is a technique that can be used to determine the vibrational energy levels of a molecule. This is because when a molecule absorbs a photon of infrared light, it is excited to a higher vibrational energy state. The energy of the photon is equal to the difference in energy between the initial and final vibrational states of the molecule.
D. Rotational spectroscopy is a technique that can be used to determine the rotational energy levels of a molecule. This is because when a molecule absorbs a photon of microwave radiation, it is excited to a higher rotational energy state. The energy of the photon is equal to the difference in energy between the initial and final rotational states of the molecule.