Question 1

When monochromatic radiation of energy 21.22 eV from a helium lamp is used to irradiate a sample of nitrogen, N2, gas in a photoelectron spectrometer, electrons are ejected with a maximum kinetic energy of 1.41  106 m s-1. Calculate the molar ionization energy of N2.

Accepted Answer

A)   4.13  103 kJ mol-1
B)   2.60  103 kJ mol-1
C)   15.5 kJ mol-1
D)   1.50  103 kJ mol-1E) All of the above
F) B) and D) D

Question 2

In an experiment to investigate the decay of photoexcited tryptophan, the observed lifetime of the excited state was measured for various concentrations of oxygen, O2, which acted as a quencher. By constructing a Stern-Volmer plot of the following data, determine the rate constant for fluorescence quenching.
 [O2]/moldm−30.020.040.060.080.10τpbs (O2) /ns1.641.180.910.740.63\begin{array}{llllll}{\left[\mathrm{O}_{2}ight] / \mathrm{mol} \mathrm{dm}^{-3}} & 0.02 & 0.04 & 0.06 & 0.08 & 0.10 \	au_{	ext {pbs }}\left(\mathrm{O}_{2}ight)  / \mathrm{ns} & 1.64 & 1.18 & 0.91 & 0.74 & 0.63\end{array}[O2​]/moldm−3τpbs ​(O2​) /ns​0.021.64​0.041.18​0.060.91​0.080.74​0.100.63​

Accepted Answer

A)   12.3 ? 10-9 mol-1 dm3 s-1
B)   2.7 ? 10-9 mol-1 dm3 s-1
C)   15.9 ? 10-9 mol-1 dm3 s-1
D)   10.7 ? 10-9 mol-1 dm3 s-1 E) None of the above
F) B) and C)

Question 3

A -* transition in hexa-1,3,5-triene, C6H8, corresponds to a separation between energy levels of 4.84 eV. Predict the wavelength of the corresponding maximum absorbance in the UV-visible spectrum of hexatriene.

Accepted Answer

A)   256 nm
B)   165 nm
C)   217 nm
D)   290 nmE) B) and D)
F) B) and C)

Question 4

For which of the following molecules are pure rotational spectroscopic transitions observed?
Benzene, C6H6, Sulfur hexafluoride, SF6, Carbon disulfide, CS2, Nitrous oxide, N2O.

Accepted Answer

A)   Benzene, C6H6
B)   Sulfur hexafluoride, SF6
C)   Carbon disulfide, CS2
D)   Nitrous oxide, N2OE) All of the above
F) A) and B)

Question 5

The lifetime of an excited electronic state is 2.9 ns in the absence of a quencher and 1.7 ns if a quencher is present. What is the quantum yield for quenching?

Accepted Answer

A)   0.83
B)   0.71
C)   0.59
D)   0.41E) B) and C)
F) B) and D)

Question 6

In an experiment to investigate the folding of tethered labelled peptides using fluorescence resonant energy transfer, the quantum yield for fluorescence of a rhodamine dye donor was found to decrease, on average, by a factor of 0.21 in the presence of a Texas red dye acceptor. Use the Förster theory of resonant energy transfer to determine the separation of the donor-acceptor pair, given that the Förster distance parameter for the rhodamine-Texas red pair is R0 = 4.4 nm.

Accepted Answer

A)   4.4 nm
B)   3.5 nm
C)   21.0 nm
D)   0.86 nmE) None of the above
F) A) and B)

Question 7

The bond length in a nitric oxide molecule, NO, is 1.15 Å. Calculate the rotational constant.

Accepted Answer

A)   322 GHz
B)   126 GHz
C)   0.591 GHz
D)   51.2 GHzE) A) and C)
F) A) and D)

Question 8

For a particular substituted stilbene dendrimer the quantum yield for fluorescence following electronic excitation is 0.14, with the observed lifetime of the excited state 4.6 ns. Calculate the rate constant for fluorescence.

Accepted Answer

A)   33  103 s-1
B)   30  106 s-1
C)   1.6  109 s-1
D)   6.4  10-10 s-1E) All of the above
F) C) and D)

Question 9

Calculate the number of vibrational normal modes in methanol, CH3OH.

Accepted Answer

A)   6
B)   9
C)   12
D)   13E) None of the above
F) C) and D)

Question 10

The rotational constant of a hydrogen fluoride, HF, molecule is 3.12  1011 s-1. Predict which transition in the rotational absorption spectrum will be most intense at a temperature of 400 K.

Accepted Answer

A)   from J = 0 to J = 1
B)   from J = 1 to J = 2
C)   from J = 2 to J = 3
D)   from J = 3 to J = 4E) A) and C)
F) A) and B)

Question 11

Boron trifluoride, BF3, has a three-fold symmetric planar equilibrium geometry with a B-F bond length of 1.30 Å. Calculate the moment of inertia for rotation about the three-fold axis of symmetry perpendicular to the molecular plane.

Accepted Answer

A)   9.63  10-19 kg m2
B)   5.33  10-46 kg m2
C)   1.60  10-45 kg m2
D)   8.00  10-46 kg m2E) C) and D)
F) B) and C)

Question 12

Spectroscopic vibration-rotation transitions in the P- and R-branches of the high-resolution infrared spectrum of hydrogen iodide, HI, are observed to be separated by a wavenumber of 6.37 cm-1. Calculate the length of the bond of a hydrogen iodide molecule.

Accepted Answer

A)   1.03 Å
B)   10.3 Å
C)   0.728 Å
D)   7.83 ÅE) A) and B)
F) A) and C)

Question 13

In the photoelectron spectrum of carbon disulfide, CS2, ionization from the highest occupied, 1g, molecular orbital results in little vibrational structure. In contrast, ionization from the next lowest occupied 1u molecular orbital results in a long vibrational progression in the 1 symmetric stretching mode of the CS2+ ion. Which of the following descriptions of the bonding in neutral CS2 best explains these observations?

Accepted Answer

A)   Both the 1g and 1u molecular orbitals of CS2 are non-bonding in character.
B)   The 1g molecular orbital of CS2 is antibonding in character and the 1u orbital is non-bonding in character.
C)   The 1g molecular orbital of CS2 is nonbonding in character and the 1u orbital is bonding in character.
D)   Both the 1g and 1u molecular orbitals of CS2 are antibonding in character.E) B) and C)
F) A) and D)

Question 14

When radiation of wavelength 495 nm from a monochromatic flash lamp of power 0.500 kW is used to irradiate a low-pressure sample of iodine vapour, I2, the rate of production of iodine atoms is 3.24  1019 s-1. Assuming that all of the photons emitted by the lamp are absorbed by the iodine vapour, calculate the quantum yield for dissociation of iodine molecules.

Accepted Answer

A)   0.026
B)   0.070
C)   0.052
D)   0.013E) A) and D)
F) A) and B)

Question 15

Calculate the angular momentum of a molecule with a rotational quantum number J = 3.

Accepted Answer

A)   √12 ℏ
B)   3ℏ
C)   9ℏ
D)   12ℏE) None of the above
F) C) and D) A

Question 16

The observed lifetime of an excited electronic state of a porphyrin-like metal complex was determined to be 0.35 ns, with rate constants for fluorescence and intersystem crossing of 0.6  109 s-1 and 1.8  109 s-1 respectively. Determine the rate constant for non-radiative internal conversion.

Accepted Answer

A)   0.5  109 s
B)   3.0  109 s-1
C)   2  10-9 s-1
D)   1.2  109 s-1E) B) and C)
F) B) and D)

Question 17

The absorbance of a solution of path length 10.0 cm that contained two cyanine dyes, A and B, was found to be 24.1 ? 103 at a wavelength of 550 nm and 21.9 ? 103 at a wavelength of 650 nm. Use the following data for the molar absorption coefficients of the dyes at these wavelengths to determine the concentration of dye A in the solution.
 ε/(105dm3 mol−1 cm−1) \quad\quad\quad\quad\quad\quad\varepsilon /\left(10^{5} \mathrm{dm}^{3} \mathrm{~mol}^{-1} \mathrm{~cm}^{-1}ight) ε/(105dm3 mol−1 cm−1)  
 550 nm650 nm Dye A 1.480.24 Dye B 0.562.29\begin{array}{lcc} &\quad\quad 550 \mathrm{~nm} & \quad\quad650 \mathrm{~nm} \	ext { Dye A } & 1.48 & 0.24 \	ext { Dye B } & 0.56 & 2.29\end{array} Dye A  Dye B ​550 nm1.480.56​650 nm0.242.29​

Accepted Answer

A)   0.008 mol dm-3
B)   0.020 mol dm-3
C)   0.015 mol dm-3
D)   0.025 mol dm-3 E) A) and B)
F) A) and C)

Question 18

For chlorine monofluoride, ClF, the harmonic vibrational wavenumber is 793.2 cm-1 and the anharmonicity is 0.0125. Calculate the wavenumber of the first vibrational overtone in the infrared absorption spectrum of chlorine monofluoride.

Accepted Answer

A)   793.2 cm-1
B)   1526.9 cm-1
C)   773.4 cm-1
D)   1586.4 cm-1E) B) and D)
F) A) and C) B

Question 19

What is the degeneracy of the rotational level with quantum number J = 6 in a linear molecule?

Accepted Answer

A)   13
B)   0
C)   1
D)   6E) B) and D)
F) A) and B)

Question 20

The harmonic vibrational wavenumber of the 32S16O isotopomer of sulfur monoxide is 1123.7 cm-1. Calculate the force constant for the sulfur monoxide bond.

Accepted Answer

A)   79.4 mN m-1
B)   794 N m-1
C)   7.94 N m-1
D)   7.94 N m-1E) A) and B)
F) A) and C)

Exam 11: Molecular Spectroscopy

When monochromatic radiation of energy 21.22 eV from a helium lamp is used to irradiate a sample of nitrogen, N₂, gas in a photoelectron spectrometer, electrons are ejected with a maximum kinetic energy of 1.41  10⁶ m s^-1. Calculate the molar ionization energy of N₂.

Correct Answer
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D

Correct Answer
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A -* transition in hexa-1,3,5-triene, C₆H₈, corresponds to a separation between energy levels of 4.84 eV. Predict the wavelength of the corresponding maximum absorbance in the UV-visible spectrum of hexatriene.

Correct Answer
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For which of the following molecules are pure rotational spectroscopic transitions observed? Benzene, C₆H₆, Sulfur hexafluoride, SF₆, Carbon disulfide, CS₂, Nitrous oxide, N₂O.

Correct Answer
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The lifetime of an excited electronic state is 2.9 ns in the absence of a quencher and 1.7 ns if a quencher is present. What is the quantum yield for quenching?

Correct Answer
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Correct Answer
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The bond length in a nitric oxide molecule, NO, is 1.15 Å. Calculate the rotational constant.

Correct Answer
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For a particular substituted stilbene dendrimer the quantum yield for fluorescence following electronic excitation is 0.14, with the observed lifetime of the excited state 4.6 ns. Calculate the rate constant for fluorescence.

Correct Answer
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Calculate the number of vibrational normal modes in methanol, CH₃OH.

Correct Answer
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The rotational constant of a hydrogen fluoride, HF, molecule is 3.12  10¹¹s^-1. Predict which transition in the rotational absorption spectrum will be most intense at a temperature of 400 K.

Correct Answer
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Boron trifluoride, BF₃, has a three-fold symmetric planar equilibrium geometry with a B-F bond length of 1.30 Å. Calculate the moment of inertia for rotation about the three-fold axis of symmetry perpendicular to the molecular plane.

Correct Answer
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Spectroscopic vibration-rotation transitions in the P- and R-branches of the high-resolution infrared spectrum of hydrogen iodide, HI, are observed to be separated by a wavenumber of 6.37 cm^-1. Calculate the length of the bond of a hydrogen iodide molecule.

Correct Answer
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Correct Answer
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Correct Answer
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Calculate the angular momentum of a molecule with a rotational quantum number J = 3.

Correct Answer
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A

Correct Answer
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Correct Answer
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For chlorine monofluoride, ClF, the harmonic vibrational wavenumber is 793.2 cm^-1 and the anharmonicity is 0.0125. Calculate the wavenumber of the first vibrational overtone in the infrared absorption spectrum of chlorine monofluoride.

Correct Answer
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B

What is the degeneracy of the rotational level with quantum number J = 6 in a linear molecule?

Correct Answer
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The harmonic vibrational wavenumber of the ³²S¹⁶O isotopomer of sulfur monoxide is 1123.7 cm^-1. Calculate the force constant for the sulfur monoxide bond.

Correct Answer
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Exam 11: Molecular Spectroscopy

When monochromatic radiation of energy 21.22 eV from a helium lamp is used to irradiate a sample of nitrogen, N2, gas in a photoelectron spectrometer, electrons are ejected with a maximum kinetic energy of 1.41  106 m s-1. Calculate the molar ionization energy of N2.

Correct AnswerverifiedD

Correct AnswerverifiedShow Answer

A -* transition in hexa-1,3,5-triene, C6H8, corresponds to a separation between energy levels of 4.84 eV. Predict the wavelength of the corresponding maximum absorbance in the UV-visible spectrum of hexatriene.

Correct AnswerverifiedShow Answer

For which of the following molecules are pure rotational spectroscopic transitions observed? Benzene, C6H6, Sulfur hexafluoride, SF6, Carbon disulfide, CS2, Nitrous oxide, N2O.

Correct AnswerverifiedShow Answer

The lifetime of an excited electronic state is 2.9 ns in the absence of a quencher and 1.7 ns if a quencher is present. What is the quantum yield for quenching?

Correct AnswerverifiedShow Answer

Correct AnswerverifiedShow Answer

The bond length in a nitric oxide molecule, NO, is 1.15 Å. Calculate the rotational constant.

Correct AnswerverifiedShow Answer

For a particular substituted stilbene dendrimer the quantum yield for fluorescence following electronic excitation is 0.14, with the observed lifetime of the excited state 4.6 ns. Calculate the rate constant for fluorescence.

Correct AnswerverifiedShow Answer

Calculate the number of vibrational normal modes in methanol, CH3OH.

Correct AnswerverifiedShow Answer

The rotational constant of a hydrogen fluoride, HF, molecule is 3.12  1011 s-1. Predict which transition in the rotational absorption spectrum will be most intense at a temperature of 400 K.

Correct AnswerverifiedShow Answer

Boron trifluoride, BF3, has a three-fold symmetric planar equilibrium geometry with a B-F bond length of 1.30 Å. Calculate the moment of inertia for rotation about the three-fold axis of symmetry perpendicular to the molecular plane.

Correct AnswerverifiedShow Answer

Spectroscopic vibration-rotation transitions in the P- and R-branches of the high-resolution infrared spectrum of hydrogen iodide, HI, are observed to be separated by a wavenumber of 6.37 cm-1. Calculate the length of the bond of a hydrogen iodide molecule.

Correct AnswerverifiedShow Answer

Correct AnswerverifiedShow Answer

Correct AnswerverifiedShow Answer

Calculate the angular momentum of a molecule with a rotational quantum number J = 3.

Correct AnswerverifiedA

The observed lifetime of an excited electronic state of a porphyrin-like metal complex was determined to be 0.35 ns, with rate constants for fluorescence and intersystem crossing of 0.6  109 s-1 and 1.8  109 s-1 respectively. Determine the rate constant for non-radiative internal conversion.

Correct AnswerverifiedShow Answer

Correct AnswerverifiedShow Answer

For chlorine monofluoride, ClF, the harmonic vibrational wavenumber is 793.2 cm-1 and the anharmonicity is 0.0125. Calculate the wavenumber of the first vibrational overtone in the infrared absorption spectrum of chlorine monofluoride.

Correct AnswerverifiedB

What is the degeneracy of the rotational level with quantum number J = 6 in a linear molecule?

Correct AnswerverifiedShow Answer

The harmonic vibrational wavenumber of the 32S16O isotopomer of sulfur monoxide is 1123.7 cm-1. Calculate the force constant for the sulfur monoxide bond.

Correct AnswerverifiedShow Answer

When monochromatic radiation of energy 21.22 eV from a helium lamp is used to irradiate a sample of nitrogen, N₂, gas in a photoelectron spectrometer, electrons are ejected with a maximum kinetic energy of 1.41  10⁶ m s^-1. Calculate the molar ionization energy of N₂.

Correct Answer
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D

Correct Answer
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A -* transition in hexa-1,3,5-triene, C₆H₈, corresponds to a separation between energy levels of 4.84 eV. Predict the wavelength of the corresponding maximum absorbance in the UV-visible spectrum of hexatriene.

Correct Answer
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For which of the following molecules are pure rotational spectroscopic transitions observed? Benzene, C₆H₆, Sulfur hexafluoride, SF₆, Carbon disulfide, CS₂, Nitrous oxide, N₂O.

Correct Answer
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Correct Answer
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Correct Answer
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Correct Answer
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Correct Answer
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Calculate the number of vibrational normal modes in methanol, CH₃OH.

Correct Answer
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The rotational constant of a hydrogen fluoride, HF, molecule is 3.12  10¹¹s^-1. Predict which transition in the rotational absorption spectrum will be most intense at a temperature of 400 K.

Correct Answer
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Boron trifluoride, BF₃, has a three-fold symmetric planar equilibrium geometry with a B-F bond length of 1.30 Å. Calculate the moment of inertia for rotation about the three-fold axis of symmetry perpendicular to the molecular plane.

Correct Answer
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Spectroscopic vibration-rotation transitions in the P- and R-branches of the high-resolution infrared spectrum of hydrogen iodide, HI, are observed to be separated by a wavenumber of 6.37 cm^-1. Calculate the length of the bond of a hydrogen iodide molecule.

Correct Answer
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Correct Answer
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Correct Answer
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Correct Answer
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A

Correct Answer
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Correct Answer
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For chlorine monofluoride, ClF, the harmonic vibrational wavenumber is 793.2 cm^-1 and the anharmonicity is 0.0125. Calculate the wavenumber of the first vibrational overtone in the infrared absorption spectrum of chlorine monofluoride.

Correct Answer
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B

Correct Answer
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The harmonic vibrational wavenumber of the ³²S¹⁶O isotopomer of sulfur monoxide is 1123.7 cm^-1. Calculate the force constant for the sulfur monoxide bond.

Correct Answer
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