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ISSN 1017-2548(Print)
ISSN 2234-8530(Online)
Volume 49, Number 2
JKCSEZ 49(2)
April 20, 2005 |
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Title |
Structural, Potential Surface and Vibrational Spectroscopy Studies of Hypophosphorous Acid in the Gas Phase and Chain Conformation. A Theoretical Study
Structural, Potential Surface and Vibrational Spectroscopy Studies of Hypophosphorous Acid in the Gas Phase and Chain Conformation. A Theoretical Study
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Author |
I. Ahmadi, H. Rahemi*, S.F. Tayyari
I. Ahmadi, H. Rahemi*, S.F. Tayyari
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Keywords |
DFT; IR, VCD, Vibrational Spectra, Isomeric Pathway, Hypo Phosphorous Acid
, DFT; IR, VCD, Vibrational Spectra, Isomeric Pathway, Hypo Phosphorous Acid
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Abstract |
Hypophosphorous acid (HPA) 분자의 구조와 진동 위치에너지 표면을 HF, MP2, DFT-B3LYP 등의 이론적인 계산 방법을 이용하여 연구하였다. HPA 분자의 체인 수를 증가시켰을 때, 계산된 진동 frequency가 실험값에 보다 근접하게 되는 현상을 관측하였다. P-O 결합에 수직인 O=P-O-H 각도의 함수로 나타낸 위치에너지 표면은 O=P-O 평면의 42.50에서 최소 에너지를 나타내며, saddle point와 복잡한 형태의 에너지 장벽을 보여준다. P-O-H의 비평면 진동운동에 대한 위치에너지 함수에 따르면 전자 바닥 함수에서는 284.87 cm-1의 위치에너지 장벽을 보여주지만, 전자 들뜬 상태에서는 위치에너지 장벽이 나타나지 않았다.
The potential energy surfaces (PES), molecular and vibrational structure of hypophosphours acid (HPA) were investigated by HF, MP2 and DFT-B3LYP level of theory using 6-31G** basis set. In order to approach solid state spectra we optimized mono-, di-, tri-, tetra- and penta-mer structures and computed frequencies and intensities of the vibrational modes of VCD and IR. It is found that by increasing the number of HPA molecules in the chain, some of calculated vibrational frequencies approach to the experimental solid state values. The potential energy surfaces of HPA are calculated in a wide range on the plane perpendicular to the P-O bond where the hydrogen can rotate 360 degree through O=P-O-H dihedral angle. A circular valley is found going up and down on the plane, the valley is centered to the continuation of P-O bond. There are two minima at angles ±42.50 to the O=P-O plane giving two mirror conformers and one saddle point in between with a height of 284.87 cm-1 at the angles 0o and a complex barrier with a height of 2089.40 cm-1 at the angle 180o to the same plane. On top of the complex barrier, there is a small well with depth of 15.65 cm-1. To study the tunneling effect and pathway between the two conformers, the molecule is considered to have CS symmetry and a symmetric double minimum potential energy well with a barrier of 284.87 cm-1 height in the middle. With the constructed potential, the torsional motion of P-O-H (Hindered Rotation) of the monomer, using variation method and harmonic oscillator wave functions is studied and IR frequencies and relative intensities of vibrational modes are calculated. Due to the width of the well and the trigonometric shape of the barrier, tunneling can occur at the ground state and the next excited state does not feel the barrier at all.
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