Infra-Red Spectroscopy of Hcl and Dcl Gas
Experiment 6
Infra-Red Spectroscopy of HCl and DCl gas
Abstract
Fourier-transform infrared spectroscopy has been very useful in helping scientists examining molecules of HCl and DCl. Because deuterium has a greater mass than hydrogen, the IR band shown for HCl is at a higher wavelength than DCl. The absorption of light in DCl was at lower frequency 1700-2200 cm-1 because D is bigger and heavier. That’s why the vibrations on the IR were shorter for DCl compared to HCl. The stretching of HCl on the IR region was around 2700-3100 cm-1. The constant vibration frequency is added to determine the bond length of isotope between HCl and DCl. From the ab-initio calculations it was showed that r = 1.29344 Ǻ for HCl.
Introduction
The purpose of this experiment is to observe the absorption of light from the stretching of the diatomic linear molecules HCl and DCl. By using the Fourier-transform infrared, or FTIR, technique, we will be able to study and obtain information about the vibrations of the H–Cl and D–Cl bonds. The first part of the experiment consists of preliminary calculations with data obtained from Gaussview. Using Gaussview, draw an HCl molecule and obtain the length of the H–Cl bond. This will be used for r when finding the moment of inertia. It is important to note that the H–Cl and D–Cl bond are the same length even though the deuterium atom weighs twice as much as the hydrogen atom. Though the bonds lengths are equivalent, the spectrum shows that the HCl can obtain a lower transmittance percentage and that DCl vibrations take place at a lower frequency. Quantum mechanics gives us the following formula for a harmonic oscillator:
[pic]
where [pic] is the vibrational frequency, h is Planck’s constant, and n is the vibrational quantum number. The rigid rotor model also applies to diatomic molecules. It can be solved in the equation below:
[pic]
where J is the rotational quantum number.
Below is a simple picture of a chlorine atom
Infra-Red Spectroscopy of HCl and DCl gas
Abstract
Fourier-transform infrared spectroscopy has been very useful in helping scientists examining molecules of HCl and DCl. Because deuterium has a greater mass than hydrogen, the IR band shown for HCl is at a higher wavelength than DCl. The absorption of light in DCl was at lower frequency 1700-2200 cm-1 because D is bigger and heavier. That’s why the vibrations on the IR were shorter for DCl compared to HCl. The stretching of HCl on the IR region was around 2700-3100 cm-1. The constant vibration frequency is added to determine the bond length of isotope between HCl and DCl. From the ab-initio calculations it was showed that r = 1.29344 Ǻ for HCl.
Introduction
The purpose of this experiment is to observe the absorption of light from the stretching of the diatomic linear molecules HCl and DCl. By using the Fourier-transform infrared, or FTIR, technique, we will be able to study and obtain information about the vibrations of the H–Cl and D–Cl bonds. The first part of the experiment consists of preliminary calculations with data obtained from Gaussview. Using Gaussview, draw an HCl molecule and obtain the length of the H–Cl bond. This will be used for r when finding the moment of inertia. It is important to note that the H–Cl and D–Cl bond are the same length even though the deuterium atom weighs twice as much as the hydrogen atom. Though the bonds lengths are equivalent, the spectrum shows that the HCl can obtain a lower transmittance percentage and that DCl vibrations take place at a lower frequency. Quantum mechanics gives us the following formula for a harmonic oscillator:
[pic]
where [pic] is the vibrational frequency, h is Planck’s constant, and n is the vibrational quantum number. The rigid rotor model also applies to diatomic molecules. It can be solved in the equation below:
[pic]
where J is the rotational quantum number.
Below is a simple picture of a chlorine atom