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Infrared spectroscopy is a nondestructive technique used in chemistry to identify compounds.
Every spectroscopic technique has its strengths and weaknesses; there isn't a single technique that excels in all areas.

Mass Spectrometry
- Best for obtaining molecular weights and fragmentation patterns.
- Key Point: Destructive method, referred to as "obliteration technology".
NMR Spectroscopy
- Perfect for examining one or two nuclei at a time and providing structural information.
- Concerns: High cost of instruments; e.g., a 60 MHz benchtop model costs approximately $100,000. Higher frequency magnets (300-400 MHz) can cost $300,000-$400,000 with significant upkeep costs (liquid helium and nitrogen needed regularly).
- Limited lifespan (10-12 years) due to possible operational issues.
Infrared Spectroscopy
- Inexpensive instruments (around $20 each) and longevity of equipment.
- Often a primary method for characterization in research (as evidenced by author's PhD work).

Typically, three techniques are employed for molecular characterization: Infrared (IR), proton NMR, and carbon NMR, along with elemental analysis.
Functionality: Infrared spectroscopy measures molecular vibrations. Heat generation from these vibrations is crucial to its functionality.
- Instruments detect heat related to bond vibrations, correlating to bond types and molecular structure.

Infrared spectroscopy focuses on vibrational modes of molecular bonds, such as:
- Two weights on a spring model.
- Three positions of motions (e.g., stretching of bonds).
Transmittance Measurement: The amount of light of a specific wavelength that passes through the sample; indicates molecular absorption.
- This is characterized in terms of percent transmittance, where lower percentages indicate higher absorption by the molecule.

The instrument operates within the infrared region of the electromagnetic spectrum, which is lower energy compared to UV spectroscopy.
Sample Preparation: ATR (Attenuated Total Reflectance) sampling can be used where samples are placed on the ATR surface for analysis.

The author describes settings like an ATR setup for sampling and highlights experiences during PhD research using infrared spectroscopy for polymer production.
Cost Ranges for Equipment: General infrared spectrometers range from $20,000 to $25,000; advanced setups can exceed $250,000 for high-speed reactions.

Spectra illustrate specific bond vibrations and are categorized into diagnostic regions:
- Bonds involving hydrogen vibrate above 2700 cm$^{-1}$.
- The fingerprint region lies below 1600 cm$^{-1}$ and is used for extensive comparison as unique absorption patterns exist here.
Wave Number Units: Infrared spectroscopy uses reciprocal centimeters as its unit of measure. Each vibrational frequency correlates to absorption of quantized light wavelengths.

Author mentioned observing the difference between a carbonate and a thiocarbonate in reaction settings, highlighting the utility of IR spectroscopy for different chemical functionalities.
Mentioned how rapid reaction tracking (e.g., a five-millisecond half-life reaction) can be performed with sophisticated setups, showcasing an advanced application of infrared spectroscopy.

The author expresses a continued reliance on infrared spectroscopy as an essential tool in chemical analysis despite its underappreciation in some circles.
Upcoming discussions in future sessions will formalize these ideas and allow further exploration into practical use and interpretation of infrared spectra.