We know how to determine the total number of vibrational modes for a molecule with a given number of atoms. If the stretching frequencies you identified are the only ones appearing in the diagnostic region, and each bond contributes one stretching mode, how many additional vibrational modes must be represented in the overlapping signals in the fingerprint region for each of these molecules?

We know how to determine the total number of vibrational modes for a molecule with a given number of atoms. If the stretching frequencies you identified are the only ones appearing in the diagnostic region, and each bond contributes one stretching mode, how many additional vibrational modes must be represented in the overlapping signals in the fingerprint region for each of these molecules?

Principles of Modern Chemistry

8th Edition

ISBN:9781305079113

Author:David W. Oxtoby, H. Pat Gillis, Laurie J. Butler

Publisher:David W. Oxtoby, H. Pat Gillis, Laurie J. Butler

Chapter20: Molecular Spectroscopy And Photochemistry

Section: Chapter Questions

Problem 30P

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We know how to determine the total number of vibrational modes for a molecule with a given number of atoms. If the stretching frequencies you identified are the only ones appearing in the diagnostic region, and each bond contributes one stretching mode, how many additional vibrational modes must be represented in the overlapping signals in the fingerprint region for each of these molecules?
Draw an energy level diagram (E vs. R) featuring a ground electronic state and two excited electronic states, one of which is bonding and one antibonding. Also clearly show vibrational and rotational energy levels. Explain what R is.
Which of the following statements about vibrational frequencies are true? (There is more than one correct answer.) Choice 1 of 3:A. A vibrational frequency corresponds to an internal movement of a molecule, such as a bond lengthening and shortening. Choice 2 of 3:B. An imaginary frequency corresponds to a molecular movement downhill from a saddle point. Choice 3 of 3:C. All molecular structures have at least one imaginary frequency.
Compute for the predicted frequency of the strongest band in the IR spectrum of molecule 3H19F, if the strongest band of molecule 2H19F has a frequency of 9.99 × 1013 Hz.
Riboflavin absorbs UV-visible light making the electrons in the molecule more energetic. As a result, the more energetic electrons move from the 'ground state' electronic energy level to higher electronic energy levels known as 'excited states’. Which of the following statements is NOT true regarding how the ‘excited state’ molecule loses energy and returns to the 'ground state'? a) non-radiative losses via bond vibration and rotation within the molecule b) non-radiative losses via phosphorescence c) non-radiative losses via collisions with other molecules d) radiative losses via fluorescence emission of light
If the spacings between adjacent vibrational features in a photoelectron spectroscopy experiment decrease, changing by a factor of 1/2, when you deuterate the molecule being ionized, is it more likely that the orbital from which you are ejecting an electron is from a nonbonding orbital, a p orbital localized on a C-C or C-O bond, or a s orbital localized on a C-H bond? Explain.
Consider the following statements as they apply to infrared spectroscopy. Decide if each is true or false. True False The quantized nature of molecular vibrations are generally understood in terms of a rigid rotor model. True False Absorption bands in infrared spectroscopy are due to vibrational and rotational-vibrational transitions in molecules. True False For a given pair of atoms, the vibrational frequency expected if they are joined by a single bond should be higher than if they are joined by a double bond. True False Because molecules in condensed phases (solids and liquid) are not free to rotate, rotational-vibrational transitions are not observed in their infrared spectra. For this reason, even at high resolution, a condensed phase spectrum is characterized by broad bands. True False Heteronuclear diatomic molecules such as HCl do not absorb infrared radiation.
Calculate the number of possible vibrational modes for each of the following molecules and assign frequency ranges to each. i) NH3 ii) C2H4 iii) CCl2F2 iv) CH3CH2OH b) Which of the above molecules will absorb IR radiations most strongly? Explain your answer.
The right-hand diagram shows electronic and vibrational levels for a diatomic molecule. Indicate which peaks in the spectrum below correspond to which vibrational transition. Explain the difference in the intensity of the vibrational peaks in the spectrum from part a. Why is the first peak the most intense?
Which of the following statements about the IR activity is true? A linear diatomic molecule composed of two identical atoms has a reduced mass of zero resulting in an infinitely high natural frequency of vibration. A linear diatomic molecule composed of different atoms will not have any IR active stretching mode. Degenerate IR active modes have the same natural frequencies of vibration A non-linear molecule composed of 17 atoms will have 45 active IR vibrational modes. IR vibrational modes typically correspond to a change in a dipole moment that is perpendicular to one of the molecules mirror planes.
Indicate whether each statement is true or false. The larger the number of atoms in a molecule, the more degrees of freedom of rotational and vibrational motion it likely has.
how would you answer this question? this is a non graded practice