The Properties of Oxygen Investigated with Easily Accessible Instrumentation

Abstract

The physical properties of oxygen, in particular, the blue color of the liquid phase, the red glow of its chemiluminescence, and its paramagnetism as shown by the entrapment or deflection of liquid oxygen by a magnetic field, can be investigated in a regular school setting with hand-held spectrophotometers and digital cameras. In college-level chemistry courses, the paramagnetic property often serves as a dramatic illustration of the usefulness of molecular orbital (MO) theory. However, MO treatment of oxygen molecules alone cannot explain the observed photon absorptions and emissions. In fact, it is the formation of oxygen dimers (O2)2 that accounts for the observed optical phenomena and is also responsible for the “not-quite-right” degree of deflection of the liquid stream of oxygen near a magnet. A review of experimental and theoretical studies of O4 and (O2)2 suggests that the so-called one-photon-two-O2-molecule mechanism be considered a one-photon-one-O2-dimer process.

Photo-excitation energy transfer between a titanium(iv)–porphyrin complex and oxygen molecule

“…Porphyrins and their metal complexes are well known as highly effective triplet state photosensitizers to be capable of producing singlet molecular oxygen, 1 O 2 ( 1 D g ), under illumination in the presence of oxygen. [9][10][11][12][13][14][15][16][17][18] Singlet oxygen is a highly reactive and electrophilic species that reacts with an electron-rich moiety, such as the double bond of ascorbate. [33][34][35] Although a number of studies have so far reported on the production of singlet oxygen molecules through the photo-excitation of porphyrins, [9][10][11][12][13][14][15][16][17][18] molecular level elucidation about how triplet oxygen interacts with porphyrins remains unsolved.…”

“…[9][10][11][12][13][14][15][16][17][18] Singlet oxygen is a highly reactive and electrophilic species that reacts with an electron-rich moiety, such as the double bond of ascorbate. [33][34][35] Although a number of studies have so far reported on the production of singlet oxygen molecules through the photo-excitation of porphyrins, [9][10][11][12][13][14][15][16][17][18] molecular level elucidation about how triplet oxygen interacts with porphyrins remains unsolved. To clarify this problem, we studied the interaction mechanism between the TiO(tpyp) complex and triplet oxygen molecule from the viewpoint of molecular orbital characteristics and potential energy changes based on the computed results.…”

“…8 A number of studies have been reported on the photo-excitation effects of porphyrins on triplet oxygen to convert it to singlet oxygen. [9][10][11][12][13][14][15][16][17][18] However, it has not yet been clear which site of the porphyrin molecule plays a predominant part in the conversion of an oxygen molecule from its triplet to singlet state, although it is important for the molecular level elucidation of how triplet oxygen interacts with porphyrin molecules.…”

Dimol Emission of Oxygen Made Possible by Repulsive Interaction

“…The red light emitted by singlet molecular oxygen is a standard textbook example of chemiluminescence, , and has a long history of experimental − and theoretical ,− investigations. The energy of the strongest band of the emitted light is approximately twice as large as that of the vertical O 2 ( a 1 Δ g ) → O 2 ( X 3 ∑ g – ) transition, which is spin-forbidden.…”

“…In case of the emission, however, the mechanism does not seem to be proven yet. Kasha in his classic paper speaks about a vaguely defined “simultaneous transition” of a pair of molecules, and many authors believe that the emission comes from dimers even at room temperature . Billington argues that dimers would not exist above 100 K, and proposes the emission to be collision induced (CIE).…”