Final answer:
Water vapor in the air has unique absorption characteristics that cause a spikey pattern of peaks in the IR spectrum at approximately 1500 cm¹ due to varying interactions of water molecules with IR radiation, resulting in a distinct fingerprint region for water.
Step-by-step explanation:
The spikey nature of peaks in the IR spectrum of air at approximately 1500 cm¹, which are attributed to water vapor, can be explained by the unique absorption characteristics of water molecules. When IR radiation is passed through the air, water molecules absorb certain wavelengths that correspond to their vibrational transitions. This results in sharp lines, also known as 'hair', which are depicted as downward peaks in the IR spectrum. Each water molecule has a slightly different interaction with IR radiation due to slight differences in their environment, such as temperature and pressure, leading to a spikey pattern rather than a single neat peak.
Across different molecules, these interactions create unique patterns in the IR spectrum—often referred to as the fingerprint region. These patterns can be used to identify the presence of specific molecules by comparing them to known standards. In the case of water, its vibrational modes result in characteristic absorption lines that lead to the spikey appearance of its peaks in the IR spectrum of air. Transmittance levels vary at these peaks, indicating how strongly water is absorbing the IR radiation at these specific wavelengths.