Carbon dioxide vibrational energy

Figure C3.3.12. The energy-transfer-probability-distribution function P(E, E ) (see figure C3.3.2 and figure C3.3.11) for two molecules, pyrazine and hexafluorobenzene, excited at 248 nm, arising from collisions with carbon dioxide molecules. Both collisions that leave the carbon dioxide bath molecule in its ground vibrationless state, OO O, and those that excite the 00 1 vibrational state (2349 cm ), have been included in computing this probability. The spikes in the distribution arise from excitation of the carbon dioxide bath 00 1 vibrational mode.

Margottin-Maclou M, Doyennette L and Henry L 1971 Relaxation of vibrational energy in carbon monoxide, hydrogen chloride, carbon dioxide and nitrous oxide App/. Opt. 10 1768-80... 

Sharma R D and Brau C A 1967 Near-resonant vibrational energy transfer in nitrogen carbon dioxide mixtures Phys. Rev. Lett. 19 1273-5... 

Yardley J T and Moore C B 1967 Intramolecular vibration-to-vibration energy transfer in carbon dioxide J. Chem. Phys. 46 4491-5... 

Infrared spectroscopy relies on a changing dipole during a bond vibration for absorption of energy to occur. In Raman, it is a change in polarizability in the bond that permits absorption. The simple molecule carbon dioxide, 0=C=0, is an instructive example. Both C=0 bonds have dipoles but they oppose each other and the net dipole is 0 Debye (OD). The symmetrical stretch in which both C=0 bonds simultaneously extend and contract does not change the dipole but is detectable by Raman because the polarizability of the system alters. 

A molecule can only absorb infrared radiation if the vibration changes the dipole moment. Homonuclear diatomic molecules (such as N2) have no dipole moment no matter how much the atoms are separated, so they have no infrared spectra, just as they had no microwave spectra. They still have rotational and vibrational energy levels it is just that absorption of one infrared or microwave photon will not excite transitions between those levels. Heteronuclear diatomics (such as CO or HC1) absorb infrared radiation. All polyatomic molecules (three or more atoms) also absorb infrared radiation, because there are always some vibrations which create a dipole moment. For example, the bending modes of carbon dioxide make the molecule nonlinear and create a dipole moment, hence CO2 can absorb infrared radiation. 

Figure 9 The normalized vibrational friction felt by a range of diatomic solutes dissolved in liquid carbon dioxide and liquid acetonitrile (62). The solutes are meant to represent the nondipolar molecule Br2 itself and two bromine mimics differing only in the replacement of the bromine quadrupole by permanent dipoles of different strengths. The d5 solute has a dipole moment of 5.476 D and the d8 solute a dipole moment of 8.762 D. (The notation r/vv emphasizes the fact that only potential-energy contributions are included in the calculations centrifugal force terms are neglected.)...

Figure 4 Vibrational line shift data for the asymmetric CO stretching mode of W(CO)6 vs. density along two isotherms of three polyatomic supercritical fluids, ethane (34°C panel a and 50°C panel b), fluoroform (28°C panel c and 44°C panel d), and carbon dioxide (33°C panel e and 50°C panel f). The data are presented as the difference between the absorption peak frequency and the gas phase (zero density) peak in cm-1. The negative sign means that the shift is to lower energy. The upper panel for each solvent is an isotherm at 2°C above the critical temperature. Error bars on each point are approximately 0.1 cm-1.

The oxidation of methane with molecular oxygen is catalyzed by the atomic platinum cation [11b]. A key step in the catalytic cycle is the reaction of PtCHi with molecular oxygen to mainly (70%) regenerate PF via liberation of neutral species [C,Hi,Oil which either represents vibrationally excited formic acid and/or its decomposition products (CO-f-HiO) and (CO2+H2). Final oxygenates are methanol, formaldehyde as well as higher oxidation products (Scheme V.4). Experimentally determined reaction energies for the elemental steps are summarized in Table V.2 [11b]. The coupling of carbon dioxide and aromatic C-H bonds mediated by ion SiFs" has also been observed [11c]. 

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