Thomas M. Dunn

Free-jet spectra and structure of o-, m- and p-dihydroxybenzenes

Abstract Analysis of the free-jet spectra of hydroquinone (para), catechol (ortho) and resorcinol (meta) shows the presence of multiple origins in each molecular spectrum which are interpreted as belonging to separate structural isomers.

Excited state spectroscopy of para di-substituted benzenes in a supersonic beam using resonant two photon ionization

Abstract Excited state vibronic spectra of p -aminophenol, p -cresol, p -fluoroaniline, p -fluorophenol, hydroquinone and p -toluidine have been obtained using resonant two photon ionization supersonic beam mass spectrometry. Despite marked similarities in the spectra, notable differences exist and different para polyatomic substituents in the same molecule show vibronic evidence of their real molecular symmetry of C 2ν . Expansion of the ring is also noted upon excitation in all cases. Further, it is now evident that the assignment of some vibronic bands historically interpreted as sequence structure must be reconsidered since molecules like hydroquinone are mixtures of cis and trans and others have a vibronic structure arising from the polyatomic nature of the substituents ( c ƒ. CH 3 ).

The ground state fundamentals of p-benzoquinone and p-benzoquinone-d4

Abstract The solid state infrared and Raman spectra of p -benzoquinone and several isotopic derivatives are reported and compared with the results of previous solution and vapor phase studies and with the results of previously published normal coordinate analyses. The vibrational assignments are discussed in terms of the vibronic activity observed in the phosphorescence spectra of the individual isotopically related quinones in several host lattices at 2°K. The infrared and Raman inactive fundamentals of p -benzoquinone- h 4 obtained from vibronic analyses of the vapor phase resonance fluorescence are reported. The six Raman active lattice modes of p -benzoquinone- h 4 and - d 4 are assigned with the aid of isotope shifts and thermal-anisotropic-motion amplitudes from previously published X-ray diffraction data.

Rotational analysis of the 7000 Å (A 3Φ→X 3Δ) electronic emission system of diatomic vanadium mononitride (VN)

The (0,0) band of the electronic emission system of the diatomic molecule VN at ∼7000 A has been generated and rotationally analyzed. The system is 3 Φr →3 Δr and is the vanadium analog of the niobium nitride system centered ∼6029 A. The constants for the upper and lower (almost certainly the ground) states have been determined, including estimates of the spin–orbit coupling constants, despite the absence of satellite bands. The subband origins are somewhat asymmetrically located, probably due to the interaction of the 3 Δ2 and the higher lying (by ∼3000 cm−1 ) 1 Δ2 state. There is no evidence of localized perturbations in any of the subbands. VN has the shortest bond length (r0 =1.566 A ) observed for any diatomic molecule containing a transition metal (apart from some hydrides). The (1,1) sequence bands have also been observed but have not been rotationally analyzed at this time.

Rotational analysis of the red electronic emission spectrum of molybdenum nitride (MoN)

Abstract A system of emission bands in the red region of the optical spectrum has been identified as due to the species MoN. The system was generated by the microwave (2450 MHz) excitation of a flowing mixture of MoCl5 and molecular nitrogen in a stream of helium but is also observed in a DC arc in air between molybdenum electrodes. One of the Q-form branches has previously been assumed to be an atomic line of Mo I. The system has been assigned as the 0, 0 band of a 4Π(a) → X4Σ−(a) transition, with a large zero-field splitting of the ground 4Σ− term (∼86 cm−1). A preliminary search has been made to detect the presence of MoN in M-type stars.

Hyperfine structure in the red emission system of NbN

A detailed study of hyperfine structure observed in the 0,0 band of the 3Φ (aβ) →3Δ (aβ) system of NbN has shown that the secondary hyperfine effects observed in this structure are not due to a perturbation in the 3Δ state but rather to the presence of a nonnegligible hyperfine effect in the 3Φ excited state. Calculations of the intensity factors corresponding to the observed transitions confirm this hypothesis and give results in excellent agreement with experiment.

The electronic absorption spectrum of crystallinechromyl chloride at 1.7°K

The spectrum of chromyl chloride, CrO 2 Cl 2 , in the region 6000 A-3800 A hasbeen obtained for the crystalline substance at temperatures down to 1.7°K. Three absorption systems have been observed, together with the start of a fourth system at λ

Rotational analysis of the red electronic emission system A3Φ → X3Δ of diatomic niobium nitride (NbN)

Abstract The (0,0) band of the red emission system of the diatomic molecule niobium nitride (NbN) has been rotationally analyzed and found to arise from an A3Φr-X3Δr transition. Constants for the two states have been determined including the magnitude of the spin-orbit coupling constants in spite of their strong numerical correlation: The electronic states involved belong to case (a) coupling and no satellite bands are observed. That these results are consistent with those of similar molecules such as ZrO and TiO is verified. The asymmetry of the energy separations of the three subsystems 3Φ4-3Δ3, 3Φ3-3Δ2, and 3Φ2-3Δ1 probably has its main origin in the perturbation of the X3Δ2(5σ4dδ) substate by the low-lying 1Δ state of the same electronic configuration. A significant line broadening for J > 60, particularly in the 3Φ2-3Δ1 (0,0) subband, has been found. It is attributed to Λ doubling or hyperfine broadening due to spin uncoupling but has not been definitively analyzed at this time. No localized perturbations have been found in any of the subbands.

Assignments of the nπ∗ singlet states of p-benzoquinone

Abstract The vapor phase fluorescence spectra of p -benzoquinone- h 4 and d 4 are reported and discussed in relation to the assignment of the low lying singlet states. The low temperature, polarized single crystal electronic absorption spectra of p -benzoquinone and several of its isotopic derivatives are reported. From the isotope shifts and band polarizations of the various vibronic origins, a detailed vibronic analysis is offered of the electronic absorption spectrum of p -benzoquinone which indicates a near degeneracy of the 1 A u and 1 B 1 g electronic states.

The emission and absorption spectra of chromyl chloride in an argon matrix at 4 K

The emission and absorption spectra of chromyl chloride (and the pureW1 isotopic species) have been obtained in an argon matrix at 4 K. In emission, two systems are obtained and these correlate with the two systems previously found in the Abelson spectrum of the pure crystal and which were analyzed as the lowest singlet and triplet systems. The emission systems have, therefore, been assigned as phosphorescence and fluorescence.