Theoretical Calculation of the OH Vibrational Overtone Spectra of 1-n Alkane Diols (n = 2鈥?): Origin of Disappearing Hydrogen-Bonded OH Peak

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• 作者：Yu-Lung Cheng ; Hui-Yi Chen ; Kaito Takahashi
• 刊名：Journal of Physical Chemistry A
• 出版年：2011
• 出版时间：June 9, 2011
• 年：2011
• 卷：115
• 期：22
• 页码：5641-5653
• 全文大小：1212K
• 年卷期：v.115,no.22(June 9, 2011)
• ISSN：1520-5215

文摘

In this theoretical study, we simulated the vibrational overtone spectrum of ethylene glycol (EG), 1鈥? propanediol (PD), and 1鈥? butanediol (BD). Using the local mode model along with the potential energy curve and dipole moment function calculated by B3LYP/6-31+G(d,p) and QCISD/6-311++G(3df,3pd), we obtained the theoretical peak position and integrated absorption coefficient. Furthermore, the vibrational spectra was simulated using a Voigt function using homogeneous and inhomogenous width obtained from quantum chemical calculation methods. Previously, Howard and Kjaergaard recorded the second and third overtone photoacoustic spectra of the three aforementioned alkane diols in the gas phase and observed that the intramolecular hydrogen bonded OH peak becomes difficult to observe as the intramolecular hydrogen bonding strength increased, that is, as the chain length was increased. In this paper we show that the disappearance of the hydrogen-bonded OH peak for the OH stretching overtone excitation for BD is partly due to the increase in homogeneous width due to the increase in the hydrogen bond strength and partly due to the decrease in the relative population of the intramolecular hydrogen-bonded conformers as the chain length is increased. This latter feature is a consequence of the unfavorable strained geometry needed to form the intramolecular hydrogen bond in longer alkane chains.