Lab Report Principles of Spectroscopy

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Principles of Spectroscopy) | |Experiment 1: Rovibrational Spectrum of Hydrogen Chloride | AIM To measure the infra-red (IR) spectrum of gaseous HCl using Fourier Transform Infra-Red (FTIR) spectrometer, and analyse the rotational fine structures. ABSTRACT The experiment aims to identify various parameters of gaseous HCl related to quantum mechanics by using high-resolution IR spectrum and graphical method of analysis. The values that are being investigated specifically are νe (equilibrium vibrational frequency), νeχe (product of equilibrium vibrational frequency and anharmonicity constant), k (force constant), B0 (rotational constant at n = 0), B1 (rotational constant at n = 1), Be (rotational constant at equilibrium internuclear distance), α (Coriolis constant) and re (equilibrium internuclear distance). The spectrum obtained shows strong fundamental absorption band approximately between 3100 and 2600 cm-1, with the origin of the band approximately at 2880 cm-1. It is also characterised by the presence of P and R branches which spreads out from the origin, with the former being present at a lower wavenumber region than the latter. In addition, double peaks are observed due to the presence of two isotopes of chlorine: 35Cl and 37Cl. INTRODUCTION One of the areas being investigated in Quantum Chemistry is the vibrational and rotational aspects of a diatomic molecule. In this experiment, the diatomic molecule studied is the gaseous HCl. In understanding the vibrational energy levels of a diatomic molecule, the molecule is first approximated to a harmonic oscillator which obeys Hooke’s Law: an approximation which states that the extension of a spring is directly

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