Spectroscopy Part 1 Flashcards
What determined the energy of a photon?
wavelength and frequency
What defines polarization in light?
Direction of its electric field
What defines polarization in light?
Direction of its electric field
What are Fraunhofer lines?
Set of spectral lines originally observed as dark features in the optical spectrum of the sun
What is the condition of resonance?
Radiation must have the same energy as a transition between two states
Why must there be equal energies between the initial and final states?
To observe absorption in an absorption vs. wavelength graph
Which needs a lot of energy: nuclear transitions or nuclear/electron spins?
Nuclear transitions (gamma rays)
True or False: the ground state is not thermodynamically stable
False: it is thermodynamically stable
How can an atom/molecule end up in an excited state?
Through the absorption of a photon, chemical reaction or including thermal energy
What is the most likely transition for a molecule?
HOMO to LUMO
What does HOMO stand for?
Highest Occupied Molecular Orbital
What does LUMO stand for?
Lowest Unoccupied Molecular Orbital
What is Ground State (S0)?
The total spin number is 0 and two electrons of opposite spin are in the HOMO
What is the 1st Excited Singlet State (S1)?
The total spin quantum number is 0 and one electron is located in the LUMO and a spin paired electron is located in the LUMO
The excited state is ________. The molecule returns to its groud state via the production of heat, light or energy transfer to another molecule (Q)
transient
What do ground state-to excited state transition energies depend on?
Molecular structure, intermolecular interactions, and local environment
Why is HOMO to LUMO the most common/likely transition state?
Because it has the lowest energy gap
What is the difference between 1st Excited Singlet State and the 1st Excited Triplet State?
1st Excited Singlet State: different spin of one electron in the HOMO and another in the LUMO
1st Excited Triplet State: same spin of one electron in the HOMO and another in the LUMO (therefore takes a while to go back to ground state due to the Pauli exclusion principle)
Why do molecular moieties likely absorb light in the 200 to 800 nm region?
Because that is the region of the UV vis spectroscopy, which is light we can see
What are chromophores?
Part of a molecular entity responsible for an absorption band and the approximate location of the corresponding electronic transition (e.g.: aromatics, alkenes, carbonyls)
Conjugation of _________ bonds tends to decrease transition energies
unsaturated
What is the Hyperchromic shift?
The strength of absorption (absorptivity)roughly doubles with each new conjugated double bond
What are auxochromes?
Chemical group that is attached to a chromophore and modifies its light absorption properties by altering the energies of the MOs
