Q1 · June 2021 · 2 marks
The correct statement from the following set (i) to (iv) is (i) if q is the displacement from equilibrium for harmonic motion, the potential energy is proportional to q (ii) if the vibrational frequency (\nu) of HCl is 2990 \mathrm{cm^{-1}}, its zero point energy will be 1495 \mathrm{cm^{-1}} (iii) the correct order of vibrational frequency of \mathrm{O{-}^{1}H} (X_1), \mathrm{O{-}^{2}H} (X_2) and \mathrm{O{-}^{3}H} (X_3) is X_1 > X_2 > X_3 (iv) the fundamental vibrational transition of a diatomic molecule appears at 1880 \mathrm{cm^{-1}}. Its first overtone will be at 940 \mathrm{cm^{-1}} (assuming anharmonicity constant as zero)
- (a) i, ii, iii only
- (b) i, ii, iii, iv
- (c) ii, iii only
- (d) i, ii, iv only
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Answer: (c)
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Q2 · June 2021 · 2 marks
The molecule that will not absorb in the microwave region, but will absorb in the infra-red region
- (a) \mathrm{N_2}
- (b) \mathrm{C_2H_2}
- (c) HCl
- (d) \mathrm{H_2O}
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Answer: (b)
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Q3 · Dec 2013 · 2 marks
The molecule with the smallest rotation partition function at any temperature among the following is:
- (a) \mathrm{CH_3{-}C{\equiv}C{-}H}
- (b) \mathrm{H{-}C{\equiv}C{-}H}
- (c) \mathrm{H{-}C{\equiv}C{-}D}
- (d) \mathrm{D{-}C{\equiv}C{-}D}
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Answer: (b)
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Q4 · June 2019 · 2 marks
The correct statements about HCl and DCl , among the following is
- (a) DCl has smaller Zero Point Energy than HCl
- (b) HCl has smaller vibrational frequency than DCl
- (c) The force constant k for HCl bond is half that of DCl
- (d) The reduced mass of DCI is smaller than that of HCl
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Answer: (a)
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Q5 · Dec 2019 · 2 marks
The frequency of O – H stretch occurs at \sim 3600\ \mathrm{cm^{-1}}. The O – D stretch frequency (in \mathrm{cm^{-1}}) would be closest to
- (a) 3000
- (b) 2600
- (c) 1800
- (d) 900
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Answer: (b)
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Q6 · Dec 2019 · 2 marks
In the pure rotational microwave spectrum of a XY molecule, the adjacent lines are separated by 4\ \mathrm{cm}^{-1}. If the molecule is irradiated by a radiation of 30{,}000\ \mathrm{cm}^{-1}, the first Stokes line(in \mathrm{cm}^{-1}) appears at
- (a) 29988
- (b) 30012
- (c) 30004
- (d) 29996
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Answer: (a)
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Q7 · 2011-2020 · 2 marks
The equilibrium dissociation energy of a diatomic molecule is 4.75 eV and its stretching frequency corresponds to 0.5 eV. The minimum energy required to dissociate the molecule in eV is
- (a) 4.75
- (b) 4.25
- (c) 4.50
- (d) 5.00
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Answer: (c)
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Q8 · Dec 2019 · 2 marks
The vibrational transition energies of a diatomic molecule corresponding to \mathrm{v}=1 \leftarrow \mathrm{v}=0 and \mathrm{v}=2 \leftarrow \mathrm{v}=1 are 2143.1 \mathrm{~cm}^{-1} and 2116.1 \mathrm{~cm}^{-1}, respectively. The anharmonic constant ( \omega_{e} \chi_{e} ) of the molecule in \mathrm{cm}^{-1} is Options:
- (a) 27
- (b) 13.5
- (c) 10
- (d) 54
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Answer: (b)
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Q9 · June 2018 · 2 marks
A symmetric top molecule, among the following, is
- (a) ethylene
- (b) Allene
- (c) butatriene
- (d) Hexatriene
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Answer: (b)
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Q10 · June 2017 · 2 marks
The first electronic absorption band maximum of a polar and relatively rigid aromatic molecule appears at 310 nm but its fluorescence maximum in acetonitrile solution appears with a large Stokes shift at 450 nm. The most likely reason for the Stokes shift is
- (a) Large change in molecular geometry in the excited state
- (b) Increase in dipole moment of the molecule in the excited state
- (c) Decrease in polarizability of the molecule in the excited state
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Answer: (b)
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Q11 · Dec 2017 · 2 marks
The molecule that will show Raman spectrum, but not IR spectrum, among the following is
- (a) \mathrm{H}_{2}
- (b) HCl
- (c) BrCl
- (d) \mathrm{CS}_{2}
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Answer: (a)
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Q12 · Dec 2017 · 2 marks
The pair that contains a spherical top and a symmetric top, among the following, is
- (a) \mathrm{CH_4, CH_2Cl_2}
- (b) \mathrm{CH_2Cl_2, CH_3Cl}
- (c) \mathrm{CH_3Cl, CH_4}
- (d) \mathrm{CH_4, C(CH_3)_4}
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Answer: (c)
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Q13 · Dec 2017 · 2 marks
The g-factors of { }^{1} \mathrm{H} and { }^{13} \mathrm{C} are 5.6 and 1.4 respectively. For the same value of the magnetic field strength, if the { }^{1} \mathrm{H} resonates at 600 MHz , the { }^{13} \mathrm{C} would resonate at
- (a) 2400 MHz
- (b) 600 MHz
- (c) 150 MHz
- (d) 38 MHz
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Answer: (c)
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Q14 · Dec 2016 · 2 marks
The rotational constant and the fundamental vibrational frequency of HBr are, respectively, 10\,\mathrm{cm^{-1}} and 2000\,\mathrm{cm^{-1}}. The corresponding values for DBr approximately are
- (a) 20\,\mathrm{cm^{-1}} and 2000\,\mathrm{cm^{-1}}
- (b) 10\,\mathrm{cm^{-1}} and 1410\,\mathrm{cm^{-1}}
- (c) 5\,\mathrm{cm^{-1}} and 2000\,\mathrm{cm^{-1}}
- (d) 5\,\mathrm{cm^{-1}} and 1410\,\mathrm{cm^{-1}}
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Answer: (d)
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Q15 · Dec 2016 · 2 marks
In a 200 MHz NMR spectrometer, a molecule shows two doublets separated by 2 ppm. The observed coupling constant is 10 Hz. The separation between these two signals and the coupling constant in a 600 MHz spectrometer will be, respectively
- (a) 600 Hz and 30 Hz
- (b) 1200 Hz and 30 Hz
- (c) 600 Hz and 10 Hz
- (d) 1200 Hz and 10 Hz
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Answer: (d)
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Q16 · June 2016 · 2 marks
In an NMR spectrometer containing a 2.5 T magnet, Larmor precession frequency of { }^{1} \mathrm{H} is 100 MHz . The radiofrequency used in this spectrometer has an associated magnetic field strength of 2.5 \times 10^{-} { }^{4} \mathrm{~T}. The duration of a 90^{\circ} pulse in this instrument is
- (a) 25 \times 10^{-6} \mathrm{~s}
- (b) 50 \times 10^{-6} \mathrm{~s}
- (c) 25 \times 10^{-5} \mathrm{~s}
- (d) 50 \times 10^{-5} s
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Answer: (a)
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Q17 · June 2016 · 2 marks
Upon application of a weak magnetic field, a line in the microwave absorption spectrum of rigid rotor splits into 3 lines. The quantum number (J) of the rotational energy level from which the transition originates is
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Answer: (a)
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Q18 · Dec 2016 · 2 marks
The transition that belongs to the Lyman series in the hydrogen-atom spectrum is
- (a) 1 s \leftarrow 4 s
- (b) 1 s \leftarrow 4 p
- (c) 2 s \leftarrow 4 s
- (d) 2 s \leftarrow 4 p
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Answer: (b)
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Q19 · Dec 2016 · 2 marks
The rotational constant and the fundamental vibrational frequency of HBr are, respectively, 10 \mathrm{cm^{-1}} and 2000 \mathrm{cm^{-1}}. The corresponding values for DBr approximately are
- (a) 20 \mathrm{cm^{-1}} and 2000 \mathrm{cm^{-1}}
- (b) 10 \mathrm{cm^{-1}} and 1410 \mathrm{cm^{-1}}
- (c) 5 \mathrm{cm^{-1}} and 2000 \mathrm{cm^{-1}}
- (d) 5 \mathrm{cm^{-1}} and 1410 \mathrm{cm^{-1}}
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Answer: (d)
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Q20 · Dec 2016 · 2 marks
Among the following, both microwave and rotational Raman active molecule is
- (a) \mathrm{CH}_{4}
- (b) \mathrm{N}_{2} \mathrm{O}
- (c) \mathrm{C}_{2} \mathrm{H}_{4}
- (d) \mathrm{CO}_{2}
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Answer: (b)
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Q21 · Dec 2016 · 2 marks
In a 200 MHz NMR spectrometer, a molecule shows two doublets separated by 2 ppm. The observed coupling constant is 10 Hz. The separation between these two signals and the coupling constant in a 600 MHz spectrometer will be, respectively
- (a) 600 Hz and 30 Hz
- (b) 1200 Hz and 30 Hz
- (c) 600 Hz and 10 Hz
- (d) 1200 Hz and 10 Hz
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Answer: (d)
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Q22 · June 2015 · 2 marks
The symmetric rotor among the following is
- (a) \mathrm{CH}_{4}
- (b) \mathrm{CH}_{3} \mathrm{Cl}
- (c) \mathrm{CH}_{2} \mathrm{Cl}_{2}
- (d) \mathrm{CCl}_{4}
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Answer: (b)
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Q23 · June 2015 · 2 marks
The nuclear g-factors of { }_{1} \mathrm{H} and { }_{14} \mathrm{~N} are 5.6 and 0.40 respectively. If the magnetic field in an NMR spectrometer is set such that the proton resonates at 700 MHz , the { }_{14} \mathrm{~N} nucleus would resonate at
- (a) 1750 MHz
- (b) 700 MHz
- (c) 125 MHz
- (d) 50 MHz
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Answer: (d)
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Q24 · June 2015 · 2 marks
The spectroscopic technique, by which the ground state dissociation energies of diatomic molecules can be estimated, is
- (a) Microwave spectroscopy
- (b) Infrared spectroscopy
- (c) UV-visible absorption spectroscopy
- (d) X-ray spectroscopy
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Answer: (b)
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Q25 · Dec 2015 · 2 marks
If the reduced mass of a diatomic molecule is doubled without changing its force constant, the vibrational frequency of the molecule will be
- (a) \sqrt{2} times the original frequency
- (b) \frac{1}{\sqrt{2}} times the vibrational frequency
- (c) twice the original frequency
- (d) unchanged
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Answer: (b)
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Q26 · Dec 2015 · 2 marks
The molecule with the smallest rotational constant (in the microwave spectrum) among the following is
- (a) \mathrm{N{\equiv}CH}
- (b) \mathrm{HC{\equiv}CCl}
- (c) \mathrm{CCl{\equiv}CF}
- (d) \mathrm{B{\equiv}CCl}
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Answer: (c)
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Q27 · Dec 2015 · 2 marks
The spectroscopic technique that can distinguish unambiguously between trans-1, 2 dichloroethylene and cis-1, 2-dichloroethylene without any numerical calculation is
- (a) microwave spectroscopy
- (b) UV-visible spectroscopy
- (c) X-ray photoelectron spectroscopy
- (d) \gamma-ray spectroscopy
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Answer: (a)
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Q28 · Dec 2015 · 2 marks
The vibrational frequency of a homo-nuclear diatomic molecule is v. The temperature at which the population of the first excited state will be half that of the ground state is given by
- (a) h v . \ln 2 / k B
- (b) h v /(\ln 2 . k B)
- (c) \ln 2 /(h v . k B)
- (d) h v \cdot \log 2 / k B
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Answer: (b)
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Q29 · Dec 2015 · 2 marks
The ^{1}\mathrm{H} NMR frequency at 1.0T is 42.4 MHz. If the gyromagnetic ratios of ^{1}\mathrm{H} and ^{13}\mathrm{C} are 27 \times 10^{7} and 6.75 \times 10^{7}\mathrm{T}^{-1}\mathrm{S}^{-1} respectively, what will be the ^{13}\mathrm{C} frequency at 1.0 T ?
- (a) 10.6 MHz
- (b) 169.6 MHz
- (c) 42.6 MHz
- (d) 21.3 MHz
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Answer: (a)
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Q30 · Dec 2014 · 2 marks
Bond lengths of homonuclear diatomic molecules can be determined with the help of both
- (a) Rotational and vibrational spectroscopy.
- (b) Rotational and rotational Raman spectroscopy.
- (c) Rotational Raman and electronic spectroscopy.
- (d) Vibrational and electronic spectroscopy.
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Answer: (c)
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Q31 · Dec 2014 · 2 marks
If the component of the orbital angular momentum along the molecular axis of a heteronuclear diatomic molecule is non-zero, the rotational-vibrational spectrum will show
- (a) P and R branches only.
- (b) P and Q branches only.
- (c) Q and R branches only.
- (d) All the P, Q and R branches
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Answer: (d)
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Q32 · June 2013 · 2 marks
In NMR spectroscopy, the product of the nuclear 'g' factor (g_N), the nuclear magneton (\beta_N) and the magnetic field strength (B_0) gives the
- (a) energy of transition from \alpha to \beta state
- (b) chemical shift
- (c) spin-spin coupling constant
- (d) gyromagnetic ratio
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Answer: (b)
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Q33 · June 2012 · 2 marks
For a diatomic molecule AB , the energy for the rotational transition from \mathrm{J}=0 to \mathrm{J}=1 state is 3.9 \mathrm{cm}^{-1}. The energy for the rotational transition from \mathrm{J}=3 to \mathrm{J}=4 state would be
- (a) 3.9 \mathrm{~cm}^{-1}
- (b) 7.8 \mathrm{~cm}^{-1}
- (c) 11.7 \mathrm{~cm}^{-1}
- (d) 15.6 \mathrm{~cm}^{-1}
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Answer: (d)
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Q34 · June 2012 · 2 marks
For the vibrational Raman spectrum of a homonuclear diatomic molecule, the selection rule under harmonic approximation is
- (a) \Delta \mathrm{v}=0 only
- (b) \Delta v= \pm 1 only
- (c) \Delta \mathrm{v}= \pm 2 only
- (d) \Delta \mathrm{v}=0, \pm 1
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Answer: (b)
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Q35 · June 2012 · 2 marks
The following data were obtained from the vibrational fine structure in the vibronic spectrum of a diatomic molecule: \omega_e = 512\ \mathrm{cm^{-1}}, \omega_e x_e = 8\ \mathrm{cm^{-1}} where \omega_e is the energy associated with the natural frequency of vibration and x_e is the anharmonicity constant. The dissociation energy (D_e) of the molecule is:
- (a) 4096 \mathrm{cm^{-1}}
- (b) 6144 \mathrm{cm^{-1}}
- (c) 8192 \mathrm{cm^{-1}}
- (d) 16384 \mathrm{cm^{-1}}
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Answer: (c)
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Q36 · Dec 2012 · 2 marks
The absorption spectrum of \mathrm{O_2} shows a vibrational structure that becomes continuum at 56875\,\mathrm{cm^{-1}}. At the continuum, it dissociates into one ground state atom (\mathrm{O_g}) and one excited state atom (\mathrm{O_e}). The energy difference between \mathrm{O_e} and \mathrm{O_g} is 15125\,\mathrm{cm^{-1}}. The dissociation energy (in \mathrm{cm^{-1}}) of ground state of \mathrm{O_2} is:
- (a) 56875/15125
- (b) 15125/56875
- (c) 7200
- (d) 41750
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Answer: (d)
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Q37 · Dec 2012 · 2 marks
The vibrational frequency and anharmonicity constant of an alkali halide are 300 \mathrm{~cm}^{-1} and 0.0025 respectively. The positions (in \mathrm{cm}^{-1} ) of its fundamental mode and first overtone are respectively.
- (a) 300, 600
- (b) 298.5, 595.5
- (c) 301.5,604.5
- (d) 290,580
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Answer: (b)
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Q38 · June 2011 · 2 marks
A molecule, AX, has a vibrational energy of 1000\ \mathrm{cm^{-1}} and rotational energy of 10\ \mathrm{cm^{-1}}. Another molecule, BX, has a vibrational energy of 400\ \mathrm{cm^{-1}} and rotational energy of 40\ \mathrm{cm^{-1}}. Which one of the following statements about the coupling of vibrational and rotational motion is true?
- (a) The coupling is stronger in BX.
- (b) The coupling is stronger in AX.
- (c) Magnitude of coupling is same in both AX and BX.
- (d) There is no coupling in both AX and BX
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Answer: (a)
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Q39 · June 2011 · 2 marks
In IR spectrum of \left[\mathrm{Co}(\mathrm{CN})_{5} \mathrm{H}\right]^{3-} the \mathrm{Co}-\mathrm{H} stretch is observed at 1840 \mathrm{~cm}^{-1}. The (\mathrm{Co}-\mathrm{D}) stretch in \left[\mathrm{Co}(\mathrm{CN})_{5} \mathrm{D}\right]^{3-} will appear at nearly
- (a) 1300 \mathrm{~cm}^{-1}
- (b) 1400 \mathrm{~cm}^{-1}
- (c) 1500 \mathrm{~cm}^{-1}
- (d) 1600 \mathrm{~cm}^{-1}.
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Answer: (a)
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Q40 · Dec 2011 · 2 marks
The uncertainty in the NMR frequency of a compound in liquid state (relaxation time = 1 s) is 0.1 Hz. The uncertainty in the frequency (in Hz) of same compound in solid state (relaxation time = 10^{-4} s) is
- (a) 10
- (b) 100
- (c) 1000
- (d) 10^{-3}
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Answer: (c)
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