Which of the following statements about IR spectrophotometry is false All homonu

Question

Which of the following statements about IR spectrophotometry is false All homonuclear diatomic molecules and atoms are invisible in FT-IR Vibrational modes such as stretching ones involve changes in bond length whi modes such as scissoring and bending involve changes in bond angle. an IR active molecule must have a net change in dipole moment due to vibration rotation of the molecules d. CO_2 and SO_2 have the same number of vibrational modes for its IR activity because both molecules have three atoms. Which of the following statements about fluorescence quantum yield is false Adding a heavy atom in the molecule will decrease the quantum yield Removing the dissolved oxygen from the sample solution will decrease the quantum yield Increasing the rigidity of molecules will increase the quantum yield Increasing the temperature will decrease the quantum yield A chemical ionization source is characterized as a_______source and a___________source. Desorption, hard Gas-phase, hard Gas-phasc, soft Desorption, soft The techniques which give complementary vibrational information are dispersive IR and FTTR UV and VIS FTIR and Raman UV-VIS and X-ray Which of the following statements about NMR is TRUE Chemical shift is independent of field strength Spin-Spin splitting is independent of field strength Sensitivity of NMR instrument is independent of field strength The multiplicity of NMR band ,s determined by the number of magnetically equivalent protons in the adjacent atoms plus one Which one of the following statements about UV-Vis instrumentation is false The resolution of a UV-Vis instrument can be increased by narrowing the slits but it will reduce the incident light intensity A double beam in space typically has a rotating half-silvered mirror to direct the entire beam alternately through the sample and reference cells A single beam instrument requires physically changing the sample and reference cuvettes The double beam in space instrument has a Michelson interferometer to combine and cause interference of the beam through the sample and the beam through the reference cells

Explanation / Answer

(2): Here (d) is false because quantum yield increases with increase in temperature.

(3): Chemical ionization is carried out in gaseous or vapor phase. Also chemical ionization is an example of soft ionization source in which we apply small anount of residual energy to form small amount of fragmentation of the subject molecule.

Hence it is characterized by a gas phase source and soft source. Hence (c) is correct.

(4): Raman spectroscopy gives complementary vibrational information to FTIR( a powerful version of IR spectroscopy), as the information provided by Raman spectroscopy may not be provided by FTIR. Hence (c) should be correct.

(5): Chemical shift is defined as the amount by which a proton resonance is shifted from TMS of the spectrometer's basic operating frequency and is measure in units of ppm. Since it only depends on the spectrometer's basic operating frequency, the chemical shift value for a particular proton always remain any field strength. Hence it is  independent of field strength. Hence (a) is correct.

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