Vibrational Spectroscopy of the CCl₄ v₁ Mode: Theoretical Prediction of Isotopic Effects

Abstract

Raman spectroscopy is a powerful experimental technique, yet it is often missing from the undergraduate physical chemistry laboratory curriculum. Tetrachloromethane (CCl 4 ) is the ideal molecule for an introductory vibrational spectroscopy experiment and the symmetric stretch vibration contains fine structure due to isotopic variations of the molecule according to C 35 Cl x 37 Cl 4−x . We report simple theoretical predictions of the fine structure, calculation of Raman differential scattering cross sections, and discussion of the inherent asymmetry in the v 1 mode resulting from the different isotopes of chlorine. All calculations and discussion are appropriate for an undergraduate physical chemistry laboratory as either an independent dry lab or a supplement to a pre-existing vibrational spectroscopy lab.

The ν3 − ν4difference band contribution to the CCl4symmetric stretch (ν1) mode

“…Modern isotopic natural abundance values for chlorine indicate that the C 35 Cl 4 peak intensity should be 78.18% of C 35 Cl 3 37 Cl 1 , yet Table shows that this peak is consistently 5–10% more intense than expected over decades of investigation on CCl 4 . Moreover, varying Raman differential scattering cross section values among isotopomers are insufficient to explain this discrepancy as calculations demonstrate that the isotopomers are essentially equal in scattering strength …”

Empirical quality criteria for the approximation of the electronic term of a diatomic molecule by the Morse formula

“…In publications, the authors highly appreciate the usefulness of this potential [2,4,10,50,62,63,64,66], the importance is often emphasized by its mention in the titles of articles. In the university teaching of molecular spectroscopy and physical chemistry, Morse's potential is given considerable attention, including in laboratory practice, and didactic materials are regularly published in specialized journals [82][83][84][85][86][87][88][89]. At the same time, in the manuals, the question is presented according to the established standardfor example, its presentation at the stage of initial analysis [90,91] does not differ much from recent monographs and textbooks [92].…”

Эмпирические Критерии Качества Аппроксимации Электронного Терма Двухатомногой Молекулы Формулой Морза

“…В публикациях авторы высоко оценивают полезность этого потенциала [2,4,10,50,62,63,64,66], важность часто подчёркивается его упоминанием в заголовках статей. В университетском преподавании молекулярной спектроскопии и физической химии потенциалу Морза уделяется значительное внимание, в том числе в лабораторном практикуме, а в специализированных журналах регулярно публикуются материалы дидактического характера [82][83][84][85][86][87][88][89]. При этом в руководствах вопрос излагается по сложившемуся стандарту -например, его изложение на этапе начального анализа [90,91] не сильно отличается от монографий и учебников последнего времени [92].…”