Podcast
Questions and Answers
What occurs to the Q peak of CO2 when the temperature increases from 240 K to 250 K at a pressure of 10 kPa?
What occurs to the Q peak of CO2 when the temperature increases from 240 K to 250 K at a pressure of 10 kPa?
- It shifts to a different wavenumber
- It decreases to 6550 m2 mole-1
- It remains constant at 6650 m2 mole-1 (correct)
- It increases to 6750 m2 mole-1
How does increasing the temperature from 240 K to 250 K affect the P peak shift at a pressure of 10 kPa?
How does increasing the temperature from 240 K to 250 K affect the P peak shift at a pressure of 10 kPa?
- It shifts from 655 cm-1 to 645 cm-1 (correct)
- It shifts from 645 cm-1 to 635 cm-1
- It remains at 655 cm-1
- It shifts from 655 cm-1 to 670 cm-1
What effect does an increase in temperature have on the rotational quantum number in the CO2 infrared absorption system?
What effect does an increase in temperature have on the rotational quantum number in the CO2 infrared absorption system?
- It decreases the rotational quantum number
- It increases the rotational quantum number (correct)
- It has no effect on the rotational quantum number
- It causes the rotational quantum number to fluctuate unpredictably
What is the relationship between temperature and the spread between the P, Q, and R peaks?
What is the relationship between temperature and the spread between the P, Q, and R peaks?
Which statement accurately describes the absorption coefficient of the CO2 15 μm fundamental vibration band at 10 kPa total pressure?
Which statement accurately describes the absorption coefficient of the CO2 15 μm fundamental vibration band at 10 kPa total pressure?
Flashcards
What is the Q-branch?
What is the Q-branch?
The central peak in the infrared absorption band of CO2, corresponding to a pure vibrational transition where the rotational quantum number remains unchanged (ΔJ = 0).
What is the P-branch?
What is the P-branch?
The envelope of lines at lower wavenumbers in the infrared absorption band of CO2, corresponding to transitions where the rotational quantum number decreases (ΔJ = -1, -2, etc.).
What is the R-branch?
What is the R-branch?
The envelope of lines at higher wavenumbers in the infrared absorption band of CO2, corresponding to transitions where the rotational quantum number increases (ΔJ = +1, +2, etc.).
How do changes in temperature, pressure, and molecular amount affect the infrared absorption band?
How do changes in temperature, pressure, and molecular amount affect the infrared absorption band?
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What is the effect of increasing temperature on the CO2 infrared absorption band?
What is the effect of increasing temperature on the CO2 infrared absorption band?
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Study Notes
CO2 Infrared Absorption
- Atmospheric molecules absorb infrared radiation at specific wavelengths due to transitions between vibrational energy levels.
- Nitrogen and oxygen do not absorb infrared radiation because they lack a permanent electric dipole moment.
- Vibrational transitions are accompanied by rotational transitions, forming characteristic 'band structures'.
- The Q-branch represents a pure vibrational transition (ΔJ = 0).
- The P and R branches correspond to rotational transitions (ΔJ = ±x).
- The spread of the P and R branches depends on the rotational energy dependence (ER = J2 + |J|).
- Changes in temperature, pressure, and concentration affect the rotational quantum number, influencing the P, Q, and R peak spread.
- Figure 1 shows the CO2 15 μm fundamental vibration band absorption coefficient (σ) at 10 kPa and 240 K, with the P, Q, and R branches.
- A 10 K temperature increase (at constant pressure) affects the absorption coefficient (Δσ).
Analysis of Statements
- Statement I: Incorrect. The provided text discusses changes in the shape and spread of the absorption bands, but does not provide numerical values like 6650 m² mole⁻¹.
- Statement II: Incorrect. The text specifies that changes in temperature affect the spread of the bands, not the position of the peaks.
- Statement III: Possible. An increase in temperature could lead to an increase in available rotational energy levels. While the exact quantitative change is not described within the text, the increase in temperature could lead to an increase in the magnitude of the rotational quantum number (J).
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Description
This quiz delves into the infrared absorption characteristics of CO2 and its vibrational transitions. It explores the role of atmospheric molecules, the significance of the P, Q, and R branches, and how temperature and pressure influence absorption coefficients. Test your understanding of these concepts and their implications in atmospheric science.
