The heats of formation (HOF) for 49 tetrazole derivatives are calculated with the density functional theory (DFT) B3LYP method by means of designed isodemic and isogyric reactions. The average absolute deviation for five compounds for which the experimental HOFs are available is less than 2 kcal/mol target accuracy of G-2 theory. It has been demonstrated that for compounds involving delocalized bonds, choosing molecules containing all of the delocalized bonds as reference compounds is an appropriate approach. The calculated HOFs indicate that most neutral 2H-isomers are more stable than the corresponding 1H-isomers whereas the 1-substituted tetrazolate anions are more stable than the corresponding 2-substituted ones. Furthermore, our results consistently show that C-substituted tetrazoles are more stable than the corresponding N-substituted isomers. Our calculated heat of formation calls into question the experimental heat of formation of 2-methyltetrazole.
Inelastic and charge transfer collisions of protons with methane molecules have been investigated in a perpendicular-plane crossed beam experiment via the detection of the scattered protons and H atoms, respectively. Time-of-flight analysis of the protons and H atoms at scattering angles 0°≤θ≤10° and collision energies 10≤E≤30 eV provided information on internal energy distributions of the CH4 and CH+4 products. Excitation of the n(ν1 ,ν3) +m (ν2 ,ν4) type vibrations, with n,m=0, 1, 2,⋅⋅⋅was found to be the most probable assignment of the observed structured energy distributions of CH4 (1 A1 ) at θ≤4°. At θ>4°, the energy transfer increases steeply up to the dissociation limit while the vibrational structure was no longer resolved. In the case of charge transfer, the observed narrow internal energy distributions corresponding to a most probable average internal energy of CH+4 of about 0.95 eV was centered at the recombination energy of the proton indicative of quasiresonant charge transfer. In addition, fragmentation of CH+4 formed in charge transfer collisions of H+ with CH4 was investigated in an independent experiment using mass spectrometric analysis to identify the individual fragment species. The relative intensities of the parent and fragment ions (i.e., of CH+4, CH+3, and CH+2) were found to be in good agreement with the known values of the appearance potentials of the fragment ions and the distribution of the CH+4 internal energy as obtained from the differential cross sections. A mechanism is proposed to explain the experimental results based on vibronic symmetry correlation theory. This mechanism deals with vibronic interactions in the compound quasimolecule CH+5 and explains the origin of the unexpected excitation of infrared inactive modes [e.g., ν2 (E)] of the tetrahedral methane. The effects of Jahn-Teller distortions of the CH+4 charge transfer product are also discussed.
The electric-quadrupole and magnetic-dipole operators of a rotating, linear molecule interacting with a radiation field are formulated, in the space-fixed and in the molecular-coordinate systems, as contractions of irreducible spherical tensors. Radiative transition probabilities are obtained for the initial and final rotation-electronic states that are in Hund's Coupling Case a or b, using the normalized rotation matrix as the separated rotational wavefunction in the Born—Oppenheimer approximation. Line-strength formulas are derived for (1) transitions between singlet Case b states, in the case of an electric quadrupole, the 1Σ—1Σ, 1Π—1Σ, 1Δ—1Σ, 1Π—1Π, 1Δ—1Π, 1Φ—1Π, 1Δ—1Δ, 1Φ—1Δ, and 1Γ—1Δ transitions; in the case of a magnetic dipole, the 1Π—1Σ, 1Π—1Π, 1Δ—1Π, 1Δ—1Δ, and 1Φ—1Δ transitions; (2) the 1Π—3Π(a) transitions; (3) the 1Π—3Π(b) transitions. The master line-strength formula as well as intensity distribution for different branches are given. In (2) and (3), some of the transitions are found to be dependent on the absolute Kronig reflection symmetry, giving, for molecules of unequal nuclei, an intensity alternation for the two Λ-doubling components. A discussion of this reflection symmetry and the inversion symmetry is given and a consistent set of molecular wavefunctions of a given symmetry is constructed for (1) singlet Case b states and triplet Case a states (2) triplet Case b states expressed as a linear combination of Case a state wavefunctions through angular momentum coupling. The rotation—vibration spectra due to these higher multipole radiations are briefly discussed. A new point of view for the possibility of ΔΛ=0 (for Λ≠0) magnetic-dipole pure rotation spectra is advanced.
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