By Amina Walcott, Emma Najdzionek, Taylor Munger

Faculty Mentor. Dr. Leanna Giancarlo

Abstract: The spectroscopic properties of hydrogen halides (HF, HCl, HBr, and HI) were investigated to observe the effect of bond length on the energy of a system, with a specific focus on increasing the bond length of HF. IR and UV-VIS spectra of hydrogen halides were generated computationally in GAMESS using the ab initio basis set SPK-DZP. Using the relationship between the energy of the particle in the one-dimensional box model, Planck’s equation, and the energy of absorbance, hydrogen halides with larger atomic radii and subsequently weaker bonds were predicted to absorb at longer wavelengths due to smaller gaps between energy levels. The wavelength of maximum absorbance for HF (shortest bond length) was 78 nm, and for HI (longest bond length) was 113 nm. The harmonic oscillator model simplifies the potential energy of a vibrating bond to a parabolic function, enabling the calculation of vibrational frequencies and prediction of IR spectra. According to this model, as bond length increased, energy decreased, with HF and HI exhibiting IR peaks at around 3,720 cm⁻¹ and 2,240 cm⁻¹, respectively. When the bond length of HF was manually increased to explore the role of bond length alone, the vibrational energies decreased. However, this decrease was more drastic than expected; as the wavenumber for HF, with a bond length of 1.300 Å was 1329.7 cm⁻¹, but the vibrational energies for HCl, with a bond length of 1.306 Å, was 2,842.21 cm⁻¹. Overall, this study provides insights into the relationship between atomic radii and the spectroscopic behavior of hydrogen halides, enhancing our understanding of their spectroscopic and vibrational properties through computational chemistry methods.