36 Questions
What happens when a molecule absorbs UV-vis light?
An electron is promoted to a higher energy molecular orbital.
What determines the type of electronic transition in a molecule?
The molecule's functional groups.
What is the lowest energy electronic transition of formaldehyde?
From n to pi*
What is the purpose of infrared and microwave radiation in spectroscopy?
To change the vibrational motion of a molecule.
What are the two types of relaxation processes from an excited state?
Vibrational and electronic relaxation.
What is the difference between fluorescence and phosphorescence?
Fluorescence involves emission of a photon, while phosphorescence involves conversion of light to heat.
What is the molecular orbital diagram for formaldehyde?
Four occupied orbitals, including a nonbonding orbital (n) and a pi antibonding orbital (π*).
What are the factors that affect the relative rates of relaxation?
The molecule's solvent and temperature.
What is the purpose of vibrational and rotational states in spectroscopy?
To identify the molecule and its electronic state.
What is the difference between fluorescence and phosphorescence lifetimes?
Fluorescence has a longer lifetime than phosphorescence.
What is the purpose of internal conversion in spectroscopy?
To convert light into heat.
What happens to formaldehyde in its excited states?
It becomes pyramidal.
What happens when a molecule absorbs UV-vis light?
An electron is promoted to a higher energy molecular orbital.
What determines the type of electronic transition in a molecule?
The molecule's functional groups.
What is the lowest energy electronic transition of formaldehyde?
From n to pi*
What is the purpose of infrared and microwave radiation in spectroscopy?
To change the vibrational motion of a molecule.
What are the two types of relaxation processes from an excited state?
Vibrational and electronic relaxation.
What is the difference between fluorescence and phosphorescence?
Fluorescence involves emission of a photon, while phosphorescence involves conversion of light to heat.
What is the molecular orbital diagram for formaldehyde?
Four occupied orbitals, including a nonbonding orbital (n) and a pi antibonding orbital (π*).
What are the factors that affect the relative rates of relaxation?
The molecule's solvent and temperature.
What is the purpose of vibrational and rotational states in spectroscopy?
To identify the molecule and its electronic state.
What is the difference between fluorescence and phosphorescence lifetimes?
Fluorescence has a longer lifetime than phosphorescence.
What is the purpose of internal conversion in spectroscopy?
To convert light into heat.
What happens to formaldehyde in its excited states?
It becomes pyramidal.
What happens when a molecule absorbs UV-vis light?
An electron is promoted to a higher energy molecular orbital
What determines the type of electronic transition a molecule undergoes?
The molecule's shape
What happens to formaldehyde's shape when it is in the S1 and T1 excited states?
It becomes pyramidal
How many occupied orbitals does the molecular orbital (MO) diagram for formaldehyde show?
Four
What is the lowest energy electronic transition of formaldehyde?
From n to pi*
What types of motion can infrared and microwave radiation change in a molecule?
All of the above
What are associated with each electronic state of a molecule?
Vibrational and rotational states
What are the types of relaxation processes from an excited state?
All of the above
What happens to a molecule after it absorbs light?
It undergoes internal conversion, intersystem crossing, and fluorescence
What does internal conversion convert light into?
Heat
What determines the relative rates of relaxation from an excited state?
The solvent's temperature and pressure
What is the difference between fluorescence and phosphorescence in terms of lifetime?
Phosphorescence has a longer lifetime
Study Notes
Fundamentals of Spectroscopy: What Happens When a Molecule Absorbs Light?
- Absorption of UV-vis light promotes an electron to a higher energy molecular orbital.
- Different types of electronic transitions require different functional groups.
- Formaldehyde in its ground state is planar, but becomes pyramidal in both S1 and T1 excited states.
- The molecular orbital (MO) diagram for formaldehyde shows four occupied orbitals, including a nonbonding orbital (n) and a pi antibonding orbital (π*).
- The lowest energy electronic transition of formaldehyde is from n to pi*.
- Infrared and microwave radiation can change vibrational, translational, and rotational motion of a molecule.
- Vibrational and rotational states are associated with each electronic state, and transitions between different states can occur.
- Relaxation processes from excited state include vibrational and rotational relaxation through collision with solvent or other molecules, and electronic relaxation through the release of a photon.
- After absorption, a molecule can undergo internal conversion, intersystem crossing, fluorescence, or phosphorescence.
- Internal conversion converts light into heat, while fluorescence and phosphorescence involve emission of a photon.
- The relative rates of relaxation depend on the molecule, solvent, temperature, and pressure.
- Fluorescence has a short lifetime (10-8 to 10-4 s), while phosphorescence has a longer lifetime (10-4 to 102 s).
Test your knowledge on the fundamentals of spectroscopy and learn what happens when a molecule absorbs light. This quiz delves into the different types of electronic transitions, vibrational and rotational motion, and relaxation processes from excited states. Discover the various ways a molecule can emit light, and the factors that affect the rates of relaxation. If you're fascinated by the science of light and molecules, this quiz is for you.
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