30 Questions
What is the process called when an electron relaxes from a higher electronic state to a lower electronic state by emitting heat?
Internal Conversion
What is the emission of a photon when an electron relaxes from the S1 → S0 state known as?
Fluorescence
Which of the following is NOT a way to stabilize the excited singlet state?
Working at high concentration of solute
What is the process of emitting radiation classified into?
Fluorescence and phosphorescence
What is the process called when molecules in electronically excited states pass to a lower electronic state by colliding with other molecules?
External Conversion
What is the result of radiationless deactivation?
Emission of heat
What is the energy level associated with the transition of π-π*?
S2
What is the characteristic of singlet state?
Paired electrons with no net magnetic moment
Why do molecules with relatively unstable excited states return to the ground state by radiationless collision deactivation?
Because they have unstable excited states
What is the characteristic of triplet state?
Unpaired electrons with magnetic moment
What is the comparative energy level of the excited triplet state versus the corresponding excited singlet state?
Lower energy level
Which type of molecules are diamagnetic?
Molecules with paired electrons
Which of the following compounds favors phosphorescence over fluorescence?
Heterocyclic compounds
What is the effect of increased temperature on fluorescence and phosphorescence?
It decreases fluorescence and phosphorescence
Why do solvents containing heavy atoms decrease fluorescence?
They enhance intersystem crossing
What is the effect of dissolved oxygen on fluorescence and phosphorescence?
It decreases fluorescence and increases phosphorescence
What type of lamp is used for scanning spectra?
High-pressure xenon lamp
What is the reason for the pH dependence of fluorescence in acidic or basic aromatic compounds?
Emission intensity and wavelength differ with pH
What is the main reason for the emission spectrum being shifted to longer wavelength?
Lower energy of emission
What is the quantum yield of highly fluorescent molecules?
Nearly one
What happens to the fluorescence when the concentration of a compound becomes too large?
Linearity is lost
What is the main reason for self-absorption of fluorescence?
Overlapping of emission and absorption peaks
What type of molecular structure is ideal for fluorescence?
Rigid, planar, and aromatic
What is the relationship between fluorescence and concentration when absorbance is less than 0.05?
Direct proportionality
What is the purpose of using a double beam instrument in instrumental analysis?
To compensate for the variation of emitted radiation with wavelength
What is the function of the wavelength selector in instrumental analysis?
To select the most intense emitted wavelength
What type of detector is used in instrumental analysis due to the low intensity of emitted radiation?
Photomultiplier type detector
Why is the detector placed at a right angle to the cuvette in instrumental analysis?
To prevent the transmitted light of excitation from being recorded
For nonfluorescent substances, what is the method used to induce fluorescence?
By chemical reaction to form a fluorescent chelate
What is the purpose of constructing a calibration curve in instrumental analysis?
To determine the concentration of an unknown sample
This quiz covers the basics of instrumental analysis, specifically molecular fluorescence spectroscopy, including luminescence, fluorescence, and phosphorescence, as well as atomic and molecular orbitals.
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