Energy levels molecular spectroscopy

Molecular photoelectron spectroscopy to connect molecular orbital energy levels to experimental measurements. 

High-resolution photoelectron spectroscopy has provided information on the energy levels and bond distance in the ion At2. Prepare a molecular orbital energy-level diagram for this ion. How would you expect the bond distance in Ar2 to compare with 198.8 pm, the bond distance in CI2 (See A. WUst, F. Merkt, J. Chem. Phys., 2004,120, 638.)... 

MICROWAVE molecular spectroscopy involves the observation and analysis of absorption transitions between molecular rotational energy levels of gas-phase molecules. These transitions between rotational levels are associated with a given vibrational state of the ground electronic state, and the transitions fall in the microwave region... 

Section 13 20 IR spectroscopy probes molecular structure by examining transitions between vibrational energy levels using electromagnetic radiation m the 625-4000 cm range The presence or absence of a peak at a charac tenstic frequency tells us whether a certain functional group is present Table 13 4 lists IR absorption frequencies for common structural units... 

Atomic and Molecular Energy Levels. Absorption and emission of electromagnetic radiation can occur by any of several mechanisms. Those important in spectroscopy are resonant interactions in which the photon energy matches the energy difference between discrete stationary energy states (eigenstates) of an atomic or molecular system = hv. This is known as the Bohr frequency condition. Transitions between... 

In the Bom-Oppenheimer picture the nuclei move on a potential energy surface (PES) which is a solution to the electronic Schrodinger equation. The PES is independent of the nuclear masses (i.e. it is the same for isotopic molecules), this is not the case when working in the adiabatic approximation since the diagonal correction (and mass polarization) depends on the nuclear masses. Solution of (3.16) for the nuclear wave function leads to energy levels for molecular vibrations (Section 13.1) and rotations, which in turn are the fundamentals for many forms of spectroscopy, such as IR, Raman, microwave etc. 

The real power of ESR spectroscopy for identification of radical structure is based on the interaction of the unpaired electron spin with nuclear spins. This interaction splits the energy levels and often allows determination of the atomic or molecular structure of species containing unpaired electrons. The more complete Hamiltonian is given in Equation (6) for a species containing one unpaired electron, where the summations are over all the nuclei, n, interacting with the electron spin. 

Ultraviolet-visible spectroscopy (UV = 200 - 400 nm, visible = 400 - 800 nm) corresponds to electronic excitations between the energy levels that correspond to the molecular orbital of the systems. In particular, transitions involving n orbital and ion pairs (n = non-bonding) are important and so UV/VIS spectroscopy is of most use for identifying conjugated systems which tend to have stronger absorptions... 

The mathematical pictures called "electron density maps" are used to determine molecular structures and the energy level diagrams are used to determine the energies of bond formation and to interpret spectroscopy data. 

Molecular spectroscopy. This spectroscopy deals with the interaction of electromagnetic radiation with molecules. This results in transition between rotational and vibrational energy levels besides electronic transitions. 

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