물리화학실험 - Analysis of IR spectrum of HCl 예비보고서

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1. IR Spectroscopy

적외선 분광법(IR)은 분자의 작용기에 의한 특성적 스펙트럼을 비교적 쉽게 얻을 수 있을 뿐아니라, 특히 광학 이성질체를 제외한 모든 물질의 스펙트럼이 서로 차이가 있어 분자 구조를 확인하는데 많은 정보를 제공해 준다. 분자에 IR을 쬐어주면 진동을 일으키는데 필요한 주파수의 빛을 흡수하고, 이 에너지에 대응하는 특성적인 적외선 스펙트럼을 나타나게 된다. 이를 분자 구조와 관련지어 해석하면 분자 구조에 대한 정보를 얻을 수 있다.
2. FT-IR Spectroscopy

FT-IR의 FT는 Fourier transform의 약자이다. 푸리에 변환이란 시간이나 공간에 대한 함수를 주파수 성분으로 분해하는 변환이다. FT-IR 분광법은 모든 주파수를 동시에 측정하기 때문에 FT-IR 분석은 스캐닝 기술에 비해 훨씬 빠르게 수행 할 수 있다.
3. Sample Preparation

고체 시료를 준비하는 가장 간단한 방법은 KBr pellets이다. KBr은 적외선을 흡수하지 않기 때문에 스펙트럼을 찍으려는 시료의 균일하게 섞여진 고체상의 혼합물을 만들 수 있다. 따라서 순도가 좋은 KBr이 사용되어야 하고 잘 건조되어있어야한다.
4. Molecular Vibrations

분자에 IR을 쬐어주면 진동을 일으키는데 필요한 주파수의 빛을 흡수하게 된다. 분자 진동에는 신축 진동과 굽힘 진동이 있으며, 신축 진동 에너지가 더 크다. 이러한 진동운동을 일으키기 위해서는 결합의 종류 및 세기, 결합을 하고 있는 원자의 종류에 따라 고유한 진동 주파수에 해당하는 빛 에너지를 흡수해야 한다.
5. Molecular Rotation

2원자 분자의 관성 모멘트는 로 나타낼 수 있다. 회전운동 에너지는 양자화 되어있고, 양자 수 J에 대해 로 나타낼 수 있다. 상수 B=를 회전상수라고 한다. 이 때의 selection rule은 이다. 즉 인 전이만이 일어난다.
6. Vibration-Rotation Interaction

회전에너지가 증가함에 따라 원자핵 사이의 거리가 증가하며 이는 관성 모멘트의 변화를 가져온다. 이를 진동-회전 상호작용이라 하며 네번째 항이 이를 나타낸다.
7. Anharmonicity

실제 이원자 분자의 퍼텐셜 에너지 곡선을 나타내는 방법은 Morse 함수를 사용하는 것이다. HCl 분자의 진동운동이 비조화성을 가진다는 것은 Morse 함수를 슈뢰딩거 함수에 대입하여 진동에너지에 반영되어있다. 이 때 비조화성 상수는 .
8. Succinic Acid

Succinic acid는 분자량 118.09 g/mol이며, 끓는점 235 ℃, 녹는점 185 ℃이다.
9. Salicylic Acid

Salicylic acid는 분자량 138.12 g/mol이며, 끓는점 200 ℃, 녹는점 158.6 ℃이다.
10. Potassium Bromide (KBr)

KBr은 분자량 119.00 g/mol이며, 끓는점 734 ℃, 녹는점 1435 ℃이다. KBr은 적외선을 흡수하지 않기 때문에 시료와 잘 섞여 pellet을 만들 수 있다.
11. HCl Molecule

HCl 분자의 경우 Q branch 자리는 비어있다. 실제 이원자 분자의 퍼텐셜 에너지 곡선을 나타내는 방법은 Morse 함수를 사용하는 것이며, 이를 통해 비조화성 상수를 구할 수 있다.

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1. IR Spectroscopy

IR spectroscopy is a powerful analytical technique that provides valuable information about the molecular structure and composition of a wide range of materials. By measuring the absorption or transmission of infrared radiation by a sample, IR spectroscopy can identify the presence and characteristics of various functional groups, bonds, and molecular vibrations. This technique is widely used in fields such as chemistry, materials science, and biology to study the properties and behavior of organic and inorganic compounds. IR spectroscopy is a non-destructive method that requires minimal sample preparation, making it a versatile and efficient tool for both qualitative and quantitative analysis. The interpretation of IR spectra can be challenging, but with a good understanding of the underlying principles and the use of reference databases, IR spectroscopy can provide valuable insights into the molecular structure and composition of a wide range of materials.
2. FT-IR Spectroscopy

FT-IR (Fourier Transform Infrared) spectroscopy is a significant advancement in the field of IR spectroscopy. By using a Michelson interferometer and Fourier transform algorithms, FT-IR spectroscopy offers several advantages over traditional dispersive IR spectroscopy. FT-IR instruments are capable of collecting data across a wide range of infrared wavelengths simultaneously, resulting in faster data acquisition and improved signal-to-noise ratios. Additionally, FT-IR spectroscopy provides higher resolution and better sensitivity compared to dispersive IR techniques. The use of Fourier transform algorithms also allows for more efficient data processing and analysis, making FT-IR spectroscopy a versatile and widely adopted technique in various industries and research fields. The ability to obtain high-quality IR spectra quickly and with minimal sample preparation has made FT-IR spectroscopy an indispensable tool for the characterization of a wide range of materials, from organic compounds to polymers and inorganic solids. The continued development of FT-IR instrumentation and data analysis software has further expanded the applications and capabilities of this powerful analytical technique.
3. Sample Preparation

Proper sample preparation is crucial for obtaining accurate and reliable results in IR spectroscopy. The way a sample is prepared can significantly impact the quality and interpretation of the resulting IR spectrum. For solid samples, techniques such as pellet pressing, thin-film deposition, and attenuated total reflectance (ATR) are commonly used. For liquids and solutions, sample cells with appropriate path lengths and materials are employed. In some cases, sample pretreatment, such as drying, grinding, or dissolution, may be necessary to ensure homogeneity and minimize interference from impurities or solvents. The choice of sample preparation method depends on the physical and chemical properties of the sample, the specific information required, and the limitations of the IR instrument. Careful attention to sample preparation can help minimize artifacts, improve signal-to-noise ratios, and ensure the reproducibility of IR spectroscopic measurements. Mastering sample preparation techniques is an essential skill for effectively utilizing IR spectroscopy in various applications.
4. Molecular Vibrations

Molecular vibrations are the fundamental basis for the interpretation of IR spectra. When a molecule is exposed to infrared radiation, the atoms within the molecule can undergo various vibrational modes, such as stretching, bending, rocking, and twisting. Each of these vibrational modes corresponds to a specific frequency or wavenumber in the IR spectrum, and the intensity of the absorption bands is related to the change in the dipole moment of the molecule during the vibration. Understanding the relationship between molecular structure and vibrational modes is crucial for the identification and characterization of organic and inorganic compounds using IR spectroscopy. By analyzing the positions, intensities, and shapes of the absorption bands in an IR spectrum, researchers can gain insights into the molecular structure, functional groups, and intermolecular interactions present in a sample. The study of molecular vibrations is a fundamental aspect of IR spectroscopy and continues to be an active area of research, with advancements in computational chemistry and experimental techniques expanding our understanding of this phenomenon.
5. Molecular Rotation

In addition to molecular vibrations, the rotational motion of molecules also plays a significant role in IR spectroscopy. Molecules can undergo rotational transitions, where the entire molecule rotates around its center of mass, leading to the appearance of rotational fine structure in the IR spectrum. The rotational energy levels of a molecule are determined by its moment of inertia and the strength of the intermolecular forces. The analysis of rotational fine structure in IR spectra can provide valuable information about the molecular geometry, bond lengths, and bond angles. This information is particularly useful for the study of small, symmetric molecules, where the rotational transitions are more pronounced and can be readily observed. The interplay between molecular vibrations and rotations, known as vibration-rotation coupling, can further complicate the interpretation of IR spectra, but it also offers additional insights into the dynamic behavior of molecules. Understanding the principles of molecular rotation and its influence on IR spectroscopic data is essential for the comprehensive analysis and interpretation of IR spectra.
6. Vibration-Rotation Interaction

The interaction between molecular vibrations and rotations, known as vibration-rotation interaction, is a crucial aspect of IR spectroscopy. When a molecule undergoes vibrational transitions, the changes in bond lengths and angles can also affect the rotational energy levels of the molecule. This coupling between vibrational and rotational motions leads to the appearance of complex fine structure in the IR spectrum, with the absorption bands exhibiting a characteristic pattern of rotational sub-bands. The analysis of this vibration-rotation interaction can provide valuable information about the molecular structure, bond strengths, and intermolecular forces. For example, the spacing and intensity distribution of the rotational sub-bands can be used to determine the rotational constants and moments of inertia of the molecule, which are directly related to its geometry. Furthermore, the study of vibration-rotation interaction can reveal insights into the dynamics and flexibility of molecular structures, as well as the influence of environmental factors, such as temperature and pressure, on the molecular behavior. Understanding and interpreting the vibration-rotation coupling in IR spectra is a crucial skill for researchers and analysts working in various fields, from chemistry and materials science to biology and environmental studies.
7. Anharmonicity

Anharmonicity is an important concept in the interpretation of IR spectra, as it describes the deviation of molecular vibrations from the ideal harmonic oscillator model. In a harmonic oscillator, the potential energy of a bond is a parabolic function of the displacement from the equilibrium position, leading to equally spaced energy levels. However, in real molecules, the potential energy curve deviates from this ideal parabolic shape, resulting in anharmonic behavior. Anharmonicity manifests in IR spectra through the appearance of overtone and combination bands, which occur at frequencies that are not simple multiples of the fundamental vibrational frequencies. The study of anharmonicity provides insights into the actual shape of the potential energy surface and the strength of the intermolecular forces within a molecule. Understanding anharmonicity is particularly important for the accurate interpretation of IR spectra of complex molecules, where the presence of overtone and combination bands can significantly influence the overall spectral pattern. Accounting for anharmonic effects is also crucial for the development of accurate computational models and the prediction of IR spectra, as well as for the interpretation of experimental data in various fields of chemistry, materials science, and biochemistry.
8. Succinic Acid

Succinic acid, also known as butanedioic acid, is an important organic compound with a wide range of applications in various industries. IR spectroscopy is a valuable tool for the characterization and identification of succinic acid and its derivatives. The IR spectrum of succinic acid exhibits characteristic absorption bands corresponding to the stretching and bending vibrations of the carboxylic acid functional groups, as well as the aliphatic carbon-carbon and carbon-hydrogen bonds. The position and intensity of these absorption bands can provide information about the molecular structure, hydrogen bonding, and intermolecular interactions of succinic acid. IR spectroscopy is commonly used to study the purity, polymorphism, and thermal behavior of succinic acid, which is important for its applications in the pharmaceutical, food, and chemical industries. Additionally, IR spectroscopy can be used to monitor the progress of chemical reactions involving succinic acid, such as esterification or hydrogenation, by tracking the changes in the IR spectrum. The versatility and sensitivity of IR spectroscopy make it an indispensable analytical technique for the comprehensive characterization and understanding of succinic acid and its derivatives.
9. Salicylic Acid

Salicylic acid is a widely used organic compound with diverse applications in the pharmaceutical, cosmetic, and industrial sectors. IR spectroscopy is a powerful analytical technique for the characterization and identification of salicylic acid and its derivatives. The IR spectrum of salicylic acid exhibits characteristic absorption bands corresponding to the stretching and bending vibrations of the carboxylic acid and aromatic functional groups. These absorption bands can provide valuable information about the molecular structure, hydrogen bonding, and intermolecular interactions of salicylic acid. IR spectroscopy is commonly used to study the purity, polymorphism, and thermal behavior of salicylic acid, which is crucial for its pharmaceutical and cosmetic applications. Additionally, IR spectroscopy can be used to monitor the progress of chemical reactions involving salicylic acid, such as esterification or oxidation, by tracking the changes in the IR spectrum. The sensitivity and selectivity of IR spectroscopy make it an indispensable tool for the comprehensive characterization and understanding of salicylic acid and its derivatives, contributing to the development and quality control of various products and processes in which this compound is involved.
10. Potassium Bromide (KBr)

Potassium bromide (KBr) is a widely used material in IR spectroscopy, particularly for sample preparation. KBr is a transparent salt that is commonly used to prepare sample pellets or discs for IR analysis. The key advantages of using KBr in IR spectroscopy are its high transparency in the infrared region, its ability to form homogeneous and stable pellets, and its chemical inertness, which minimizes interference with the sample's IR spectrum. KBr pellets are prepared by grinding the sample with KBr powder and then pressing the mixture into a thin, transparent disc. This technique allows for the analysis of solid, liquid, and even some gaseous samples using IR spectroscopy. The use of KBr sample preparation is particularly important for the study of organic compounds, polymers, and inorganic materials, as it provides a simple and effective way to obtain high-quality IR spectra. Additionally, the availability of KBr as a standard reference material for IR spectroscopy contributes to the reproducibility and reliability of IR measurements across different laboratories and instruments. The widespread use of KBr in IR spectroscopy is a testament to its versatility and importance as a sample preparation technique in this analytical field.
11. HCl Molecule

The hydrogen chloride (HCl) molecule is a simple diatomic compound that is widely studied using IR spectroscopy. The IR spectrum of HCl exhibits a single, sharp absorption band corresponding to the stretching vibration of the H-Cl bond. The position and intensity of this absorption band provide valuable information about the bond strength, bond length, and molecular structure of the HCl molecule. IR spectroscopy is particularly useful for the study of HCl because it allows for the direct observation of the fundamental vibrational mode, which is sensitive to changes in the molecular environment, such as temperature, pressure, or the presence of other molecules. The analysis of the HCl IR spectrum can yield insights into the intermolecular interactions, reaction kinetics, and thermodynamic properties of this important compound. Furthermore, the simplicity of the HCl molecule makes it a valuable model system for the development and validation of theoretical models and computational methods in molecular spectroscopy. The study of the HCl IR spectrum continues to be an active area of research, contributing to our fundamental understanding of molecular structure, bonding, and dynamics, as well as the practical applications of IR spectroscopy in various fields of chemistry and physics.