Measuring the Rotational Constants of 4-Fluorophenol Using Fourier-Transform Microwave Spectroscopy
School Name
South Carolina Governor's School for Science & Mathematics
Grade Level
12th Grade
Presentation Topic
Chemistry
Presentation Type
Mentored
Abstract
We sought to determine the structure of the chemical 4-fluorophenol using microwave spectroscopy. When a photon in the microwave frequency range interacts with a molecule, there is a transition between rotational energy levels. By sending photons of varying frequencies, we were able to measure a spectrum of transitions. Furthermore, molecules rotate differently based on how their mass is spread apart in the x, y, and z planes. This distribution of mass, called the moment of inertia, determines three rotational constants, each of which correspond to how the molecule rotates. Lastly, we determined the centrifugal distortion constant to account for the bond stretching caused by the molecular rotation. Our method consisted of measuring the 8-18 GHz spectrum using chirped microwave pulses. The chirped microwave pulse is broadcast into a low-pressure vacuum chamber, where it interacts with the molecule, and the energy transitions are measured. After measuring an experimental spectrum, we used the program Gaussian to perform ab initio calculations and create a theoretical spectrum for 4-fluorophenol. We then used fitting software to assign lines from the theoretical transitions to the experimental ones until a low overall error was achieved. We concluded that the rotational and distortion constants were the following: A = 5625.610(36) MHz, B = 1454.67600(30) MHz, C = 1155.99820(49) MHz, DJ = 0.0340(42) kHz with an overall RMS error of 0.0017 MHz.
Recommended Citation
Lindsay, Grace and Pedapolu, Theophilus, "Measuring the Rotational Constants of 4-Fluorophenol Using Fourier-Transform Microwave Spectroscopy" (2020). South Carolina Junior Academy of Science. 291.
https://scholarexchange.furman.edu/scjas/2020/all/291
Location
Furman Hall 108
Start Date
3-28-2020 11:45 AM
Presentation Format
Oral Only
Group Project
Yes
Measuring the Rotational Constants of 4-Fluorophenol Using Fourier-Transform Microwave Spectroscopy
Furman Hall 108
We sought to determine the structure of the chemical 4-fluorophenol using microwave spectroscopy. When a photon in the microwave frequency range interacts with a molecule, there is a transition between rotational energy levels. By sending photons of varying frequencies, we were able to measure a spectrum of transitions. Furthermore, molecules rotate differently based on how their mass is spread apart in the x, y, and z planes. This distribution of mass, called the moment of inertia, determines three rotational constants, each of which correspond to how the molecule rotates. Lastly, we determined the centrifugal distortion constant to account for the bond stretching caused by the molecular rotation. Our method consisted of measuring the 8-18 GHz spectrum using chirped microwave pulses. The chirped microwave pulse is broadcast into a low-pressure vacuum chamber, where it interacts with the molecule, and the energy transitions are measured. After measuring an experimental spectrum, we used the program Gaussian to perform ab initio calculations and create a theoretical spectrum for 4-fluorophenol. We then used fitting software to assign lines from the theoretical transitions to the experimental ones until a low overall error was achieved. We concluded that the rotational and distortion constants were the following: A = 5625.610(36) MHz, B = 1454.67600(30) MHz, C = 1155.99820(49) MHz, DJ = 0.0340(42) kHz with an overall RMS error of 0.0017 MHz.
