Methane, CH4

Methane, the smallest hydrocarbon, is an uncolored and non-smelling gas. It has a symmetrical nonpolar structure, where the carbon atom is surrounded by four hydrogen atoms in a perfectly tetrahedral arrangement.

CH4, methane molecule model from Wikipedia.

CH4 is regarded as non-toxic for humans but may displace oxygen in a closed space and cause a risk for suffocation.

Normally the gas is formed in swamps or other oxygen-poor environments such as soil, manure or sewage plants. Other major methane sources are mining, processing and use of coal, oil and natural gas. The IR spectrum of methane is less complicated than spectra from larger hydrocarbons because it has a simpler structure.

Unfortunately, methane is a powerful greenhouse gas and should not come out in the atmosphere, unless in very small concentrations. Methane emissions are expressed in carbon dioxide equivalents using its global warming potential (GWP). Then one kg CH4 is more than 20 times as effective at trapping heat in the earth´s atmosphere as one kg of CO2, within a time horizon of 100 years.

SenseAir field device for methane detection in soil. The soil quality strongly influences the evaporation of methane, dinitrogen oxide and other greenhouse gases.


IR spectrum of methane, CH4

In the IR spectrum of methane there are two strong absorption bands consisting of many overlapping peaks. They are found at 3020 cm-1 (3.3 µm) and 1300 cm-1 (7.7 µm) due to C-H stretching and bending modes, respectively.

Other hydrocarbons also have peaks from C-C bonds but not methane since it has only one carbon per molecule.

A detailed IR transmission spectrum of methane, CH4. There is a strong absorption where the transmission level goes down. This IR spectrum is copied from Wikipedia.