Microwave Spectroscopy Senior Project Abstracts
An Investigation of Low Temperature Ammonia-Helium Collisions: State-to-State Cross Sections
Mark Delaney, 2006
State-to-state cross sections for the (2,2) ammonia rotational inversion transition were measured through collisions with helium at the temperatures of 7.0 K, 8.0K, and 9.0K. The measured cross sections were then compared with theoretical calculations predicted by three potential surfaces using MOLSCAT. As was expected, the results did not agree with theoretical calculations. However, trends in previous studies seem to lend validity to the measurements reported here in terms of the magnitude of the measured cross sections compared to that of the predicted cross sections. A direct contrast was also observed between measured results and theory with respect to the behavior of the measured cross sections with increasing temperatures.
An Investigation into Low Temperature Collisions: Carbonyl Sulfide-Helium
Bryan Lyssy, 2006
We have performed quantum scattering calculations to determine if varying long range values of a theoretical OCS-He potential surface will lead to an appropriate change in energy-dependent pressure broadening cross sections, and subsequently temperature-dependant pressure broadening cross sections. A theoretically ab initio potential surface for interactions between carbonyl sulfide (OCS) and helium (He) was used due to its easily changeable parameters. The original potential surface for the broadening of the J=2<-1 rotational transition of OCS was compared to the same potential surface, but with a 10% decrease in that data corresponding to 7.0 Angstroms and beyond. We hope to use and make slight changes to this ab initio potential surface in order to determine if this method will cause the theoretical temperature-dependent cross sections at lower temperatures from a previous experiment, to agree better to the experimental results.
Experimental Investigation of Collision Induced Rotational Intra-Doublet Energy Transfer Rate of NH3 by He at 8 K
Michael Dean, 2005
Experiments were conducted examining the rate that NH3 inversion transitions occur through collisions with He at a temperature of 8 K. Measurements of inversion transitions were found between intra-doublet rotational energy levels of (1,1) and (2,2). Measured rates were compared with theoretically calculated rates done using quantum scattering techniques and previously measured cross sections found by way of He pressure broadening, As with what was found earlier, measured rates did not precisely match with any calculated rates. Associations formulated seem to show that the values of the state-to-state rate found are relatively reasonable.
An Investigation into Low Temperature Collisions: Ammonia - Helium
Joseph Ribaudo, 2005
We have performed quantum scattering calculations to predict the pressure broadening collisional cross sections, the energy and temperature dependant collisional cross sections, and the transitional rate coefficients for the (j,k)=(1,1) and (j,k)=(2,2) inversion transitions of ammonia in the low temperature interaction of ammonia (NH3 ) molecule with helium (He). The calculations were done over low temperatures ranging from 1-50 K for three different potential surfaces. It is hoped that the results of this paper, when compared to experimental data, will determine which of these surfaces most accurately predicts the interactions between ammonia and helium in the low temperature-low energy regime.
Low Temperature Energy Transfer Studies of Ammonia-Helium Collisions
Ibrahim Sulai, 2004
Using microwave spectroscopy, we investigated a number of processes at play in low temperature collisions between ammonia (NH3) and helium (He). In particular, attempts were made to measure the collisionally induced relaxation rates for an inversion doublet that had a significant fraction of the population excited to the upper inversion level. It was discovered however that there was insufficient power to cause the required saturation of the transitions of interest. Consequently, measurements for determining the best saturation conditions and of maximizing the power transmitted into the collision cell were made. The framework for the attempted double resonance experiments and for interpreting the observations are reported.
Preparation of the TEA Carbon Dioxide Laser to Excite Ammonia Molecules
Matthew Stairiker, 2003
Through this experimentation process we have found that the radiation produced by the TEA CO2 Laser is attenuated in various ways. The goal was to attain an output power that is comparable to that of the Das and Townes experiment. The reason for this is Das and Townes performed a similar experiment that dealt with the excitation of the ammonia molecule and were successful. Once the alignment was finished we did obtain enough power, theoretically, inside the vacuum chamber to perform the excitation experiment.
Measuring Collision Rates of NH3 and He/H2 using IR-MW and MW-MW Double Resonance Experiments
Jeremy Trombley, 2003
No abstract available.
Integrating the TEA CO2 Laser with the Low Temperature Molecular Spectroscopy Experiment
Jeremy Snyder, 2001
For three years now, the TEA CO2 Laser has been sitting in the optics lab at Allegheny College. The main goal has been to prep the laser so it can be integrated with the Low Temperature Molecular Spectroscopy Experiment. The LTMS Experiment measures the collision rates between NH3, He, and H2 (Willey, 1997). By incorporating the TEA Laser Dr. Willey will be able to excite the NH3 molecules out of the ground state. He will then measure the relaxation rate of the molecule back to the ground state. The ammonia relaxes through collisional energy transfer with other molecules such as H2 and He (Willey, 1997). These measurements will deliver more information about interstellar clouds in outer space. Before incorporating the TEA Laser with the LTMS Experiment, mylar windows were tested against the power of the CO2 beam. The CO2 radiation will have to pass through this type of window to reach the cell where the ammonia gas mixture is. If the windows did not allow enough energy through or did not hold up to the power of the laser, then the LTMS Experiment set up would have to be altered.
Making a TEA CO2 Laser Tunable
Ryan Hamilton, 2000
No abstract available.
Low Temperature Parahydrogen Pressure Broadening of Ammonia Inversion Transitions
Danielle Wesolek, 2000
In order to examine molecular collisions between ammonia and parahydrogen at low temperatures the collisional-cooling technique is used. Microwave spectroscopy plays an essential role in interpreting the interactions of these molecules since the energy difference between rotational levels and the inversion doublets of the ammonia molecule correspond to the microwave region of the spectrum. The focus of my experiment is on the transitions between the inversion doublets for two J=K inversion levels: (1,1) and (2,2) at temperatures between 20 and 33K. Through the use of the collisional-cooling technique and microwave spectroscopy, ammonia pressure broadening data are determined experimentally and are used to evaluate theoretical calculations. In addition, a comparison between the parahydrogen pressure broadening cross-sections of ammonia's (1,1) and (2,2) inversion doublets obtained in this experiment and those of normal hydrogen and helium pressure broadening cross-sections attained in previous experiments are shown.
The Collisional Rate Ratio of the Ammonia Molecule by Collisional Cooling
Ryan Wig, 2000
No abstract available.