Carbon dioxide cation plays an important role in the dynamics of plasma discharges and chemistry of planetary atmospheres [25]. Multiple ionization of the
molecule (CO
n þ
2 ) might also occur in collisional processes that might be followed
by Coulomb explosion (Eq. 7.5), that is, the fragmentation of the molecular ion into
two or three atomic ions [26].
CO
n þ
2
! C
p þ
þ O
q þ
þ O
r þ
ð7:5Þ
7.2 Spectroscopic Techniques Applied to the CO 2 States
7.2.1 Infrared (and Raman) Spectroscopy
The vibrational (and rotational) spectra of carbon dioxide have been extensively
investigated for
• their relevance to the study of planetary atmosphere [27];
• recording of CO 2 level in the air and analysis of remote sensing data; and
• detecting the bonding state of the COO moiety in chemicals and materials [28, 29].
The linear triatomic molecule in its ground state exhibits four normal vibration
modes (Fig. 7.7) according to the (3N–5) rule, where N is the number of atoms in
the molecule. While the antisymmetric stretching (m 3 ) and the doubly degenerate
bending (m 2 ) modes are IR-active, the symmetric stretching mode (m 1 ) is IR-inactive
(but is active in Raman spectroscopy), as this normal mode does not generate any
change of the electric dipole-moment of the molecule. In the IR spectrum of free
(gaseous) CO 2 , the antisymmetric stretching frequency (m 3 ) is found at
2349.16 cm
−1
, [30a] while it is found at 2344.0 cm
−1 in the solid state (15 K)
[30b]. In aqueous solution, this stretching (2343 cm
−1 ) is shifted by only 6 cm
−1
from the vapor phase, indicating the absence of hydrogen bonding between water
molecules and dissolved CO 2 [30c]. The infrared absorption attributed to the
bending vibration of the molecule is observed at 667.38 cm
−1 for gaseous CO 2 [30]
and at 654.7 and 659.8 cm
−1 for solid CO 2 , with a full width at half maximum of
symmetric stretching
bending (doubly degenerate)
antisymmetric stretching
ν 1
ν 2
ν 3
Fig. 7.7 Normal vibration modes of the carbon dioxide molecule in its ground state. Reprinted
from Ref. [5b], Copyright (2016), with permission from Elsevier
7.1 Electronic Properties of CO 2
111
molecule (CO
n þ
2 ) might also occur in collisional processes that might be followed
by Coulomb explosion (Eq. 7.5), that is, the fragmentation of the molecular ion into
two or three atomic ions [26].
CO
n þ
2
! C
p þ
þ O
q þ
þ O
r þ
ð7:5Þ
7.2 Spectroscopic Techniques Applied to the CO 2 States
7.2.1 Infrared (and Raman) Spectroscopy
The vibrational (and rotational) spectra of carbon dioxide have been extensively
investigated for
• their relevance to the study of planetary atmosphere [27];
• recording of CO 2 level in the air and analysis of remote sensing data; and
• detecting the bonding state of the COO moiety in chemicals and materials [28, 29].
The linear triatomic molecule in its ground state exhibits four normal vibration
modes (Fig. 7.7) according to the (3N–5) rule, where N is the number of atoms in
the molecule. While the antisymmetric stretching (m 3 ) and the doubly degenerate
bending (m 2 ) modes are IR-active, the symmetric stretching mode (m 1 ) is IR-inactive
(but is active in Raman spectroscopy), as this normal mode does not generate any
change of the electric dipole-moment of the molecule. In the IR spectrum of free
(gaseous) CO 2 , the antisymmetric stretching frequency (m 3 ) is found at
2349.16 cm
−1
, [30a] while it is found at 2344.0 cm
−1 in the solid state (15 K)
[30b]. In aqueous solution, this stretching (2343 cm
−1 ) is shifted by only 6 cm
−1
from the vapor phase, indicating the absence of hydrogen bonding between water
molecules and dissolved CO 2 [30c]. The infrared absorption attributed to the
bending vibration of the molecule is observed at 667.38 cm
−1 for gaseous CO 2 [30]
and at 654.7 and 659.8 cm
−1 for solid CO 2 , with a full width at half maximum of
symmetric stretching
bending (doubly degenerate)
antisymmetric stretching
ν 1
ν 2
ν 3
Fig. 7.7 Normal vibration modes of the carbon dioxide molecule in its ground state. Reprinted
from Ref. [5b], Copyright (2016), with permission from Elsevier
7.1 Electronic Properties of CO 2
111