Document Type

Honors Paper

Advisor

Jacob Stewart

Publication Date

2026

Abstract

A high-resolution absorbance spectrum of 1-butene was obtained in the 994–1000 cm⁻¹ region using a quantum cascade laser-based spectrometer coupled with a supersonic jet expansion source. To mitigate the low number density of the molecular jet, a multi-pass optical configuration was employed to achieve an effective path length of approximately six passes. Experimental spectra were calibrated using a methanol reference and etalon. Supporting calculations for vibrational frequencies and rotational constants were performed at the MP2/cc-pVTZ level of theory. The observed spectral features were assigned to the vibrational band ν25 (centered at 993.67 cm⁻¹), which was identified as a primarily a-type transition. The experimental data was fitted to a theoretical spectrum generated in PGOPHER; by refining the excited-state rotational constants, a preliminary fit was achieved with an average residual of 0.009 cm⁻¹ across 45 transitions. These results provide the precise molecular constants necessary for accurate spectral simulations across varying temperatures and pressures, supporting applications in atmospheric monitoring and astrochemistry. Future improvements suggest utilizing a Herriott cell to further increase the path length and transitioning to a pre-mixed gas-phase sample of 1-butene in argon to enhance the signal-to-noise ratio.

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The views expressed in this paper are solely those of the author.