Carbon dioxide absorbs infrared energy during bending or stretching motions that are accompanied by a change in dipole moment (from zero). Which of the transitions pictured of Major Technique 1 on the website of this book can absorb infrared radiation? Explain your reasoning. See Box 8B.1.

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Box 8B.1 WHAT HAS THIS TO DO WITH... THE ENVIRONMENT? THE GREENHOUSE EFFECT The Sun acts like a black body (Topic 1B), emitting radiation with a peak in intensity at 500 nm, in the visible region of the spectrum. About 55% of the solar radiation that falls on the Earth is reflected away or used in natural processes. The remain- ing 45% is converted into thermal motion (heat). Because the Earth also behaves a little like a black body, it radiates energy. Because the temperature of Earth is lower than that of the Sun, most of this energy escapes as infrared radiation with wave- lengths between 4 and 50 m. The greenhouse effect is the trapping of this infrared radia- tion by certain gases in the atmosphere. This effect warms the Earth, as if the entire planet were enclosed in a huge green- house*. Oxygen and nitrogen, which make up roughly 99% of the atmosphere, do not absorb infrared radiation. However, water vapor and CO do. Even though these two gases make up only about 1% of the atmosphere, they trap enough radiation to raise the temperature of the Earth by 33 C. Without this natu- rally occurring greenhouse effect, the average surface tempera- ture of the Earth would be well below the freezing point of water. Relative intensity of radiation at surface HO 400 CO 8 CH 800 1200 Wavenumber, >/cm- HO 1600 MAPATH 2000 The intensity of infrared radiation at various wavenumbers that would be lost from Earth in the absence of greenhouse gases is shown by the smooth line. The jagged line is the intensity of the radiation actually emitted.