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TEST TEMA 1 ESPECTRO
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Preguntas del test (64)
1 A molecule has three energy levels (A, B and C). Level A is the fundamental one and levels B and C correspond to excited states with life times of 10-6and 10-9s, respectively. The band corresponding to the transition A-->C is wider than that of the transition A-->B.
- AVerdadero
- BFalso
2The rotational spectrum of a given diatomic molecule will be shifted to higher frequencies when going from the rigid to the non-rigid rotator model.
- AVerdadero
- BFalso
3 A quantum mechanical system has energy levels depending on a single quantum number, expressed as El=A(l+1)(l−1) , with l=1,2,3,... and A>0. The selection rule for electric dipole-allowed transitions reads Δl=±1. Which of the following expressions renders the energy gap for an allowed transition:
- AΔE(l+1←l)=2Al+1
- BΔE(l+1←l)=2l+A
- CΔE(l+1←l)=2Al+A
- DΔE(l+1←l)=2l+1
4Which of the following factors is guaranteed to affect the WIDTH of a spectral line?
- AThe temperature
- BThe transition probability
- CThe wavelength of the transition
- DThe optical path through the sample
5A microwave spectrum of a diatomic gas sample registers a set of lines whose spacing gets smaller as the line frequency increases. Which of the following statements are true?
- AThe molecule has no permanent dipole moment
- BThe molecule has permanent dipole moment
- CThe molecule behaves as a rigid rotor
- DThe molecule behaves as a non-rigid rotor
6About the rotation of diatomic molecules we can state that:
1) The energy separation between two consecutive rotational levels in the rigid-rotator approximation is constant and equal to 2B .
2) The energy separation between two consecutive rotational levels in the non-rigid rotator approximation is non-constant and larger than 2B .
3) The centrifugal distortion correction applied in the non-rigid rotor model decreases when the rotational quantum number increases.
4) The rotational constant B is proportional to the inertia moment of the molecule.
Trieu-ne una:- A2 and 4
- B1
- C1, 2 and 4
- Dnone of the other answers is correct
7In the rigid rotator model the potential energy of the rotating system is considered constant.
- AVerdadero
- BFalso
8Which of these statements about Raman radiation scattering is true?
Trieu-ne una:- ARaman transitions are only possible if the molecule possesses a permanent dipole moment
- BAnti-Stokes lines denote a process where the material system has increased its energy during the interaction with radiation
- CStokes lines appear with a wavelength that is longer than the wavelength of the incident light
- DRayleigh and anti-Stokes lines are sometimes not detected
9Indicate which of the following statements about the rotational spectrum of a mixture of two isotopologues, 14N16O and 15N16O, are correct when considering the rigid-rotor model:
- AThe spacing between the bands corresponding to each individual molecule will be constant
- BThe bands corresponding to the heavier 15N16O molecule will appear at higher frequencies.
- CThe spacing between the bands of the lighter molecule will be smaller than that for the heavier molecule.
- DThe difference in frequency between two identical transitions for both molecules increases with J .
10The rotational constant of the 1H35Cl molecule is larger than the one of the isotopologue 1H37Cl ( Re = 1.287 Å ).
- AVerdadero
- BFalso
11 A given diatomic has a rotational constant of 3.4 cm-1. What is the distance between lines that will be observed in a Raman rotational spectrum?
- A3.4 cm-1
- B7.2 cm-1
- C10.2 cm-1
- D13.6 cm-1
12Linear polyatomic molecules have two different moments of inertia and the third equal to 0.
- AVerdadero
- BFalso
13Doppler band broadening in liquid and gas samples increases as temperature increases
- AVerdadero
- BFalso
14The wavelength of radio waves is longer than that of microwaves and much longer than that of Ultraviolet waves.
- AVerdadero
- BFalso
15The rotational spectra of 1HCl and 2HCl are registered and compared. Which of the following statements is false?
- AAt a given temperature, the spectrum that shows more lines is that of 2HCl
- BJmax(1HCl)>Jmax(2HCl)
- CB(1HCl)>B(2HCl)
- Dr(1HCl)>r(2HCl)
16 Increasing temperature increases the intensity of all absorption bands in spectroscopy.
- AVerdadero
- BFalso
17Which of the following general statements on the principles of spectroscopy is NOT TRUE?
Trieu-ne una:- AThe number of bands observed in a spectrum is smaller than the number of potential transitions
- BTransitions starting at the ground state are always the most intense
- CSpectra registered at lower temperature have narrower bands
- DAbsorption and emission spectra obey the same selection rules.
18The energy of the Stokes Raman radiation is higher than that of the anti-Stokes one.
- AVerdadero
- BFalso
19Which of the following statements on general principles of spectroscopy are correct?
1) The number of signals observed is normally less than the number of potential transitions. This is because of the selection rules.
2) The intensity of a given band depends on the population of the starting quantum level.
3) Reducing the temperature will cause the width of the band to increase.
4) The absorption observed is proportional to the optical path through the sample and its concentration.
Trieu-ne una:- A1, 2 and 4
- B2 and 4
- C1, 3 and 4
- Dall of them
20Spontaneous emission of radiation is the physical principle behind the laser effect.
- AVerdadero
- BFalso
21 Indicate which of the following statements about the rotational spectra of a 1:1 mixture of HCl (r = 1.279 Å) and CO (r = 1.128 Å) are correct:
1) Based on the bonding types, the rigid rotor will be as good model for HCl as for CO.
2) The most intense line (Jmax) is higher for HCl than for CO.
3) CO will give bands at higher energies than HCl.
4) The centrifugal distortion constant (D) is the same for both gases.
Trieu-ne una:- A1, 2
- B3, 4
- C2
- Dnone of the other answers is correct.
22Indicate which of the following statements about the rotational spectra of a 1:1 mixture of HCl (r = 1.279 Å) and CO (r = 1.128 Å) are correct:
1) Based on the bonding types, the rigid rotor will be as good model for HCl as for CO
2) The most intense line (Jmax) is higher for HCl than for CO
3) CO will give bands at higher energies than HCl.
4) The centrifugal distortion constant (D) is the same for both gases.
Trieu-ne una:- A1, 2
- B3 and 4
- C2
- Dnone of the other statements is true
23The microwave spectrum of a diatomic molecule begins with these two lines: 16.9 cm-1 and 32.1 cm-1. Which of the following statements is true?
Trieu-ne una:- AThe rotational constant is 8.45 cm-1
- BThe rotational constant is 16.9 cm-1
- CThe rotational constant is 32.1 cm-1
- DThe rigid rotor model is not applicable to this molecule
24The acquisition of spectra is faster in dispersive than in FT spectroscopy.
- AVerdadero
- BFalso
25The most populated state is always the ground state.
- AVerdadero
- BFalso
26Indicate which of the following statements about the scattering of light (laser in the microwave part of the electromagnetic spectrum) by a rotating nitrogen molecule are correct:
1) Both Raman and Rayleigh types of radiation will be detected.
2) Nitrogen molecules giving rise to Raman Stokes lines will increase their energy.
3) Anti-Stokes Raman lines will appear at lower frequencies than the incident radiation.
4) Rayleigh scattered radiation obeys ΔJ = 0 as selection rule and is several orders of magnitude more intense than its Raman counterparts.
Trieu-ne una:- A1, 4
- B1, 2 and 4
- C3, 4
- DNone of the other answers is correct.
27In a spectrum we observe the transitions from the ground state of the system to two excited states A and B. If the half-width at half-maximum (HWHM) of the peak that corresponds to the transition to the A state is larger than that of the peak corresponding to the transition to the B state, we can affirm that:
Trieu-ne una:- AThe lifetime of B is shorter of the one of A
- BThe lifetime of A is shorter of the one of B
- CThe energy of the transition to A is two times the one of the transition to B
- DNone of the other answers is correct
28 Consider the scattering of LASER light by a rotating fluorine molecule and indicate which of the following statements are correct:
1) Stokes Raman lines arise from fluorine molecules increasing their rotational state in two units.
2) Anti-Stokes Raman lines follow ΔJ = +2 as selection rule.
3) Anti-Stokes Raman lines will be slightly more intense than their Stokes counterparts.
4) The molecule will give Raman spectrum.
Trieu-ne una:- A3 and 4
- B1 and 4
- C1, 3 and 4
- Dnone of the other statements is true
29Population inversion is only obtained for two energy level systems at long pumping times.
- AVerdadero
- BFalso
30Which of the following general statements on the principles of Raman scattering do apply?
1) Selection rules in Raman scattering are the same as in absorption spectroscopy.
2) Raman scattering is less intense than Rayleigh scattering.
3) Stokes lines appear at higher frequency than anti-Stokes lines.
4) Detectors in Raman are placed at 90º from the incoming beam of radiation.
Trieu-ne una:- A2, 4
- B1, 2
- C3, 4
- D1, 3
31Doppler band broadening in liquid and gas samples increases as temperature increases.
- AVerdadero
- BFalso
32Consider the rotation of the SF6 (octahedral) molecule and indicate which of the following statements are correct:
1) The molecule is classified as a spherical rotor given that the three perpendicular moments of inertia defined about its center of mass are unequivalent.
2) The molecule is classified as a symmetric rotor.
3) Low intensity rotational bands can be observed due to the weak dipolar moment generated by centrifugal distortion.
4) No rotational bands are observed due to its zero dipolar moment.
Trieu-ne una:- A1, 4
- B2, 3
- C2, 4
- Dnone of the other answers is correct
33 A tetrahedral (spherical) polyatomic rotor does not present rotational spectrum given its null dipolar moment.
- AVerdadero
- BFalso
34The line of maximum intensity (Jmax) of a given rotational spectrum can be shifted by means of the working temperature.
- AVerdadero
- BFalso
35Imagine that you have two excited states with different energy, A and B. If the transition from the ground state to A appears at longer wavelengths than the transition from ground state to B, we can expect
Trieu-ne una:- AThe band corresponding to the transition of ground state to A to be thinner than to B
- BThe band corresponding to the transition of ground state to B to be thinner than to A
- COne of the two transitions to be forbidden
- DNone of other answers is correct
36Symmetric rotors present three different moments of inertia.
- AVerdadero
- BFalso
37 What is the degree of degeneracy of level J=10 in a non-rigid rotator?
Trieu-ne una:- A1
- B10
- C20
- D21
38 Indicate which of the following statements about the interaction of EM radiation with a two-energy level (1 and 2, with E1 < E2) material system are correct:
1) The system reaches equilibrium when the rates of population (induced absorption) and depopulation (spontaneous + induced emission) of the ground state 1 balance.
2) Only the Einstein coefficient A determines the rate at which state 2 is depopulated through Spontaneous Emission.
3) The lower the frequency of a transition between 1 and 2, the higher the rate of depopulation of state 2 through spontaneous emission.
4) Temperature is a key parameter that influences the initial rates of the absorption and emission processes taking place.
Trieu-ne una:- A1, 2 and 4
- B1 and 4
- C3 and 4
- Dnone of the other answers is correct
39Population inversion (needed for laser radiation) is easily obtained in high-frequency energy states such as, for instance, electronic states
- AVerdadero
- BFalso
40Consider two energy states A and B (the first more stable than the second). The system is excited in a way that the populations of each state become equal. We can state that:
Trieu-ne una:- AThere will not be transitions from A to B and consequently, no energy absorption.
- BThere will be the same number of transitions from A to B than from B to A and, therefore, no net energy absorption.
- CThere will not be absorption due to lack of transitions
- DNone of the other answers is correct.
41The elastic collision of electromagnetic radiation with matter is responsible of Raman scattering.
- AVerdadero
- BFalso
42An ideal two-level system is in thermal equilibrium at room temperature. A beam of light of frequency satisfying the Bohr frequency condition is fired at the material system. What processes are possible in these circumstances?
Trieu-ne una:- AIf the system is in thermal equilibrium no process will take place.
- BAbsorption
- CAbsorption and induced emission
- DAbsorption, induced emission and spontaneous emission.
43Doppler broadening is mainly important in solid samples.
- AVerdadero
- BFalso
44 Indicate which of the following statements about the rotational spectra of a mixture of H35Cl and H37Cl are correct, when considering the rigid-rotor model:
1) A calculation of the rotational constants will show that B (H37Cl) is smaller than B (H35Cl)
2) The intensity of the bands observed is independent of the relative proportions of the two isotopologues
3) The spacing between equivalent bands of each isotopologue increases with J
4) A frequency downshift is observed for the heavier isotope due to its higher centrifuge distortion.
Trieu-ne una:- A1, 2
- B1, 2 and 4
- C1, 3
- Dnone of the other statements are true
45If in a diatomic molecule AB the rotational transition J = 2 → 3 takes place at λ = 2 cm, the transition 5 →6 (assuming the rigid rotor model) will appear at λ
= 1 cm.- AVerdadero
- BFalso
46 Consider a sample kept at 0 K. Which of the following spectroscopic processes can take place in these conditions?
Trieu-ne una:- ASpontaneous emission
- BInduced absorption
- CInduced emission
- DNone of them
47Rayleigh radiation is forbidden by the selection rules of rotational Raman spectroscopy
- AVerdadero
- BFalso
48Of the following possible causes of line broadening in spectroscopy, which one cannot be reduced (alleviated) in practice?
Trieu-ne una:- APreassure broadening
- BLifetime broadening
- CDoppler broadening
- DAll of the other options can be reduced to some degree in practice
49Indicate which of the following statements about LASERs is correct?
Trieu-ne una:- ATwo-energy level LASERs are the most common.
- BSmall stimulated emission and population inversion are required for their generation.
- CPopulation inversion is easier to attain in energy states of high frequency.
- DNone of the reported answers is correct
50The population distribution of a two-level energy system tends to 0.5 for each level at very low temperatures.
- AVerdadero
- BFalso
51Centrifugal distortion increases with the angular velocity of a rotating molecule.
- AVerdadero
- BFalso
52Wavenumber and energy are not directly proportional.
- AVerdadero
- BFalso
53 Linear polyatomic molecules have two different moments of inertia and the third equal to 0.
- AVerdadero
- BFalso
54 Consider the rotation of a polyatomic ML4 (tetrahedral) molecule and indicate which of the following statements are correct:
1) The molecule is classified as a symmetric rotor given that the three perpendicular moments of inertia defined about its center of mass are equivalent.
2) The molecule is classified as a spherical rotor given that the three perpendicular moments of inertia defined about its center of mass are equivalent.
3) Low intensity rotational bands can be observed due to the weak dipolar moment generated by centrifugal distortion.
4) No rotational bands are observed due to its zero dipolar moment.
Trieu-ne una:- A1 and 3
- B2, 3
- C2, 3 and 4
- DNone of the other answers is correct.
55Spontaneous emission of radiation dominates over induced emission for long wavelength transitions.
- AVerdadero
- BFalso
56Oblate symmetric rotors present two equal moments of inertia.
- AVerdadero
- BFalso
57A hypothetical material system follows this expression for the energy: E=(n+1)2. Transitions obey the following selection rule: ΔE=±1. Which expression will the energy of the transitions n+1←n
Follow?
Trieu-ne una:- AΔE = 2n +3
- BΔE=2n+2
- CΔE=(n+1)2
- DNone of the reported answers is correct
58 Rotational Raman Stokes and anti-Stokes lines are of similar intensity.
- AVerdadero
- BFalso
59 Which of the following molecules will show pure rotational spectra?
H2 HCl N2O CH4 CO
Trieu-ne una:- AH2
- BCO, H2
- Call of them
- DHCl, N2O, CO
60A given diatomic has a rotational constant of 3.4 cm-1. What is the distance between lines that will be observed in a Raman rotational spectrum?
Trieu-ne una:- A3.4 cm-1
- B7.2 cm-1
- C10.2 cm-1
- D13.6 cm-1
61What is always true in relation to the rotational spectrum of a diatomic?
Trieu-ne una:- AWhen temperature increases the number of lines in the spectrum increases
- BWhen temperature increases the space between lines decreases
- CCentrifugal distortion is important at large rotational quantum numbers and results in lines getting farther apart
- DThe only condition to observe a transition is that the change in quantum number is ΔJ=±1
62When temperature tends to infinity the population of each of the two states of a two energy level system tends to 0.5
- AVerdadero
- BFalso
63 The microwave spectrum of a diatomic molecule begins with these two lines: 16.9 cm-1and 32.1 cm-1. Which of the following statements is true?
Trieu-ne una:- AThe rotational constant is 8.45 cm-1
- BThe rotational constant is 16.9 cm-1
- CThe rotational constant is 32.1 cm-1
- DThe rigid rotor model is not applicable to this molecule.
64The degeneracy for the rotational energy level J=2 is 5.
- AVerdadero
- BFalso
Información
- Descripción
- Test sobre TEST TEMA 1 ESPECTRO, creado por Mel Alves el 30/07/2019.
- Autor
- Mel Alves
- Idioma
- Español
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- 3
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