FTIR Tutorial

Quiz 1 - FTIR Theory

--------------------------------------------------------------------------------
Question 1
How is the wavelength controlled in an FTIR spectrometer?
a. By a Michelson Interferometer
b. By a computer
c. By a laser
d. By calibration with a standard sample

The wavength is very accurately controlled by a laser.

--------------------------------------------------------------------------------
Question 2
What type of technique is FTIR spectroscopy?
a. A dispersive technique?
b. An emission technique
c. An absorbance technique
d. A UV-Vis technique
e. A reflectance technique

FTIR is an absorbance technique.

--------------------------------------------------------------------------------
Question 3
How is the detector on the Mattson RS/1 FTIR spectrometer cooled?
a. With water
b. With liquid nitrogen
c. With a fan
d. By Peltier cooling
e. It's not.

It has a room temperature detector.

--------------------------------------------------------------------------------
Question 4
What does the spectrum of Nitrogen(N2) look like?
a. The same as that of air
b. It has only p- and r-branches
c. The same as that of carbon monoxide
d. It doesn't have one!

There is no dipole change for vibration of N2, therefore it has no spectrum.

--------------------------------------------------------------------------------
Question 5
What are the selection rules for FTIR absorption?

A: Absorption only occurs for symmetrical molecules

B: Absorption only occurs with a dipole change

C: Absorption requires an odd vibrational quantum number

D: Absorption requires promotion to a new quantum level

1. C and D
2. All A,B,C AND D
3. A and D
4. A, B and C
5. B and D

Infrared absorption requires a dipole change for the vibration, AND sufficient energy to promote the molecule to a new vibrational quantum state.

--------------------------------------------------------------------------------
Question 6
What occurs when the moving mirror in an FTIR spectrometer is the same distance from the beamsplitter as the static mirror?
a. Constructive interference
b. Destructive interference
c. Radio interference
d. The spectrum is measured

When the 2 mirrors are at the same distance, the infrared travel the same distance, and therefore constructive interference occurs.

--------------------------------------------------------------------------------
Question 7
Which infrared technique can measure two spectra at once?
a. FTIR spectroscopy
b. FTIR-ATR spectroscopy
c. Dispersive infrared spectroscopy
d. FTIR microscopy
e. none

FTIR is single-beam wheras dispersive is double beam.

--------------------------------------------------------------------------------
Question 8
Which spectrometer is the more complicated: dispersive or FTIR?
a. Dispersive
b. FTIR
c. neither

The FTIR is much more complicated than most dispersive spectrometers

--------------------------------------------------------------------------------
Question 9
In what region of the spectrum does infrared radiation occur?
a. At the low-energy end
b. Between the visible and ultraviolet regions
c. Between the visible and microwave regions
d. Between the visible and x-ray regions
e. At the high-energy end

Infrared is just lower in energy than visible light. It occurs between the visible and microwave regions.

--------------------------------------------------------------------------------
Question 10
What occurs when a molecule absorbs infrared radiation?
a. It warms up
b. It flies around
c. It spins faster
d. It vibrates faster
e. It emits light

Either c or d. In this course we discuss vibrational spectroscopy, but rotational spectroscopy is also possible.