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Matrix Isolation Spectroscopy in Solid Parahydrogen: A Primer
Published in Leonid Khriachtchev, Physics and Chemistry at Low Temperatures, 2019
As a homonuclear diatomic molecule, H2 lacks a permanent electric dipole moment, so an isolated molecule has no electric dipole allowed rotational or vibrational transitions.2 The absorptions in Fig. 2 are not the ~10−6 weaker electric quadrupole allowed transitions, but arise due to intermolecular interactions in the condensed phase.4,8,9,11 The occurrence of these absorptions at transition energies approximated by simple sums of the gas-phase H2 vibration and rotation energies confirms the nearly free nature of the pH2 molecules in the solid. The selection rules in the solid involve the combined symmetry of both the crystal and the pH2 molecule.4,13 Thus, the IR spectrum encodes information about the environments occupied by the pH2 molecules.
Chemical Bond II: Molecular Orbitals
Published in Franco Battaglia, Thomas F. George, Understanding Molecules, 2018
Franco Battaglia, Thomas F. George
Moreover, as any homonuclear diatomic molecule, the H2+ molecule is symmetric under the exchange between the nuclei, i.e., is symmetric under reflections on the plane perpendicular to the internuclear axis through the midpoint between the nuclei. This implies that MOs may be chosen either symmetric or anti-symmetric under this symmetry. MOs symmetric about the molecular symmetry center are labeled by the letter g (gerade, which in German means even), whereas those antisymmetric are labeled with the letter u (ungerade, which in German means odd). Finally, it is customary to denote with an asterisk the anti-bonding MOs. The ground-state electronic configuration of the H2+ molecule is then denoted as (1σg)1, whereas the configuration where the electron occupies the first excited level is denoted as (1σu*)1.
Statistical Physics
Published in Rolando M.A. Roque-Malherbe, Adsorption and Diffusion in Nanoporous Materials, 2018
is the rotational partition function for a two-atom homonuclear rotor molecule, where I is the rotor moment of inertia. A two-particle rotor consist of particles of mass m constrained to remain at a fixed distance from each of them [1,2]. The rotational partition function for N atomic molecule with three axis of rotation is [10]. () qR=π12σi∏i3N−6(8π2IikTh2)12
Structure and dynamics of HD+ in the vicinity of the H+ + D and D+ + H dissociation thresholds: Feshbach resonances and the role of g/u-symmetry breaking
Published in Molecular Physics, 2022
Maximilian Beyer, Frédéric Merkt
The Hamiltonian of HD differs from that of the homonuclear species H and D only through the additional term , which vanishes in homonuclear molecules and is the only term in Equation (1) that is not invariant to the symmetry operations of the D point group. Specifically, is not invariant with respect to the permutation of the nuclei a and b and has C symmetry. This term causes a mixing of states of g and u symmetry (see, e.g. Refs. [2,12]) and couples ionisation channels differing in core rotational-angular-momentum quantum number and electron-orbital-angular-momentum quantum number l by [13,14]. Because of the mass ratio of H to D (and T), the nonadiabatic g/u-symmetry breaking in HD (and HT) is stronger than in any other isotopically substituted homonuclear diatomic molecule.
Beyond the helium buffer: 12C− 2 rotational cooling in cold traps with H2 as a partner gas: interaction forces and quantum dynamics
Published in Molecular Physics, 2021
Barry Mant, Jan Franz, Roland Wester, F. A. Gianturco
The interaction of C with molecular hydrogen, the most abundant molecule in the universe, may also be of importance in astronomical environments where it has been suggested that C could be present as neutral C is abundant in interstellar space [36], comet tails [37] and is a common component of carbon stars [38,39]. The large electron affinity of C and strong electronic absorption bands of C [5] suggests that the anion could also be detected in space [40] but as yet no conclusive evidence of its presence has been found [41–43]. As the most abundant isotopologue C is a homonuclear diatomic molecule, it does not exhibit a pure ro-vibrational spectrum making its detection in emission difficult but transitions to and from low-lying excited electronic states may allow for the anions detection. The rotationally inelastic collisions considered here between C and H serve as a complement to our earlier work on C/He collisions, the latter partner gas being the second most abundant gas in astronomical environments [31].
Electron-molecule scattering in a bichromatic elliptically polarised laser field: Plateau structures and two-centre interference minima
Published in Molecular Physics, 2021
K. Kavazović, A. Čerkić, D. B. Milošević
For a homonuclear diatomic molecule A thecontinuum-continuum matrix element in (5) has the form where is the Fourier transform of the scattering potential at the atomic centre A. The interference minima appear if this matrix element is equal to zero, which is fulfilled for . This leads to the destructive-interference condition For , (8) gives where is the equilibrium internuclear distance, is the polar angle of the molecular orientation and is the scattering angle. From this it follows that the single-scattering two-centre interference minima appear at the energy values .