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Molecular Spectroscopy - Most Important Questions! (Download PDF)
1. If the internuclear distance (i.e bond length) of a carbon monoxide molecule is 1.13 Å, then calculate the energy in eV. The atomic masses are: 12C = 1.99 × 10–26 kg; 16O = 2.66 × 10–26 kg.
A. 4.76×10-4
B. 4.76×10-3
C. 2.78×10-4
D. 2.78×10-3
2. The pure rotational (microwave) spectrum of the gaseous molecule CN consists of a series of equally spaced lines separated by a distance of 3.7978 cm–1. Calculate the internuclear distance (i.e., equilibrium bond length) of the molecule. The molar masses are: 12C = 12.011 mol–1 and 14N = 14.007 g mol–1.
- 130 pm
- 121 pm
- 117 pm
- 290 pm
3. The pure rotational (microwave) spectrum of gaseous HCl consists of a series of equally spaced lines separated by 20.80 cm–1. Calculate the internuclear distance of the molecule. The atomic masses are:
1H = 1.673 × 10–27 kg and 35Cl = 58.06 × 10–27 kg.
- 135 pm
- 129 pm
- 146 pm
- None of the above
4. Calculate the approximate value of Jmax for a rigid diatomic molecule for which the rotational constant is 1.566 cm–1 at 300 K.
- 10
- 12
- 11
- 8
5. For HCl, the fundamental vibrational frequency is 2,890 cm–1. Calculate the force constant of this molecule. The atomic masses are 1H = 1.673 × 10–27 kg; 35Cl = 58.06 × 10–27 kg.
- 500 Nm-1
- 483 Nm-1
- 789 Nm-1
- 654 Nm-1
6. A sample was excited by the 4358 Å line of mercury. A Raman line was observed at 4447 Å. Calculate the Raman shift in cm–1.
- 580
- 760
- 460
- 640
7. At what wavelength in Å would the anti-stokes line appear in the Raman spectrum of the sample excited by the 4358 Å line of mercury. A Raman line was observed at 4447 Å.
- 6238
- 4272
- 5678
- 3456
8. In a certain fluxional molecule, two groups that are interchanged by the conversion have vibrational absorption bands observed at 1650 cm–1 and 1655 cm–1. Calculate by using the Heisenberg uncertainty principle, the minimum lifetime of the states for which the separate absorptions could be distinguished.
- 0.2 ps
- 0.9 ps
- 0.5 ps
- 0.8 ps
9. Determine the NMR frequency (in MHz) of the proton (1H) in a magnetic field of intensity 1.4092 tesla, given that gN = 5.82 and μN = 5.05 × 10–27 J T–1.
- 90
- 75
- 60
- 25
10. At the coalescence temperature 331 K, the frequency separation between the two NMR signals of N, N-dimethylacetamide is 10.85 Hz. Determine the value of the rate constant for the first-order chemical exchange of the two methyl groups.
- 24.1 s-1
- 32.1 s-1
- 42.5 s-1
- 34.8 s-1
Solutions
Solution 1:
Solution 2:
Solution 3:
Solution 4:
Solution 5:
Solution 6:
Solution 7:
Solution 8:
Solution 9:
Solution 10:
ANSWER KEY
- A
- C
- B
- D
- B
- C
- B
- C
- C
- A
Download Important Questions on Molecular Spectroscopy - Download PDF Here
Check Out:
- Most Important and Expected Questions for CSIR-NET Chemical Science 2021 Exam
- Chemical Science Formula Sheets for CSIR-NET [Free] - All Important Formulas at One Place!
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