Vibrational relaxation cross sections and rates of equilibration in electronically excited benzene (2537 Å excitation)

Logan, L. M.; Buduls, I.; Knight, A. E. W.; Ross, I. G.

doi:doi:10.1063/1.438983

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Polymorphism of crystalline poly(hydroxymethyl) compounds. III. The structures of crystalline and plastic tris(hydroxymethyl)aminomethane

Between 5 °K and its m.p. (446.0 °K), tris, H2NC(CH2OH)3, exhibits one phase transition, at 407.3 °K, to form the orientationally disordered (plastic) phase I. The ordered form, phase II, is orthorhombic, Pn21a, a=8.844(1) Å, b=7.794(1) Å, c=8.795 (1) Å, Z=4, Dx=1.327 g/cm3, and Dm=1.320 g/cm3. The crystal structure can be described in terms of layers of molecules approximately normal to the c axis, with strong intralayer hydrogen bonding and weak interlayer hydrogen bonding. The crystal structu...

Collisional ionization of Cs and K by O₂

Collisional ionization of Cs and K atoms by O2 has been studied in a crossed beam geometry from threshold to ∼100 eV alkali laboratory system energy. The energy spectra of forward directed positive (Cs+ and K+) and negative (O− and O−2) ions were measured by electrostatic energy analysis. The dominant O−2 negative ion is associated with forward scattering of the alkali positive ion in the center‐of‐mass system but O− production appears associated with backward scattering of the alkali ion.

The fluorescence spectrum of benzene vapor, excited to a vibrational level 6²1¹ of the ¹B_2u state by Hg 2537 Å, has been studied in the presence of up to 600 Torr of 16 different added gases. Benzene‐d₆ has been similarly studied in the presence of N₂ and CO₂. Low pressure data yield cross sections (which are of the order of hard sphere) for the process 6²1¹→ other vibrational states which conform with the expectation of H. M. Lin, M. Seaver, K. Y. Tang, A. E. W. Knight, and C. S. Parmenter, [J. Chem. Phys. 70, 5442(1979)] that such cross sections should be determined by the intermolecular well depths. High pressure data yield efficiencies in respect of bringing about vibrational equilibration. Estimated average energies lost per hard sphere collision are broadly determined by the number of degrees of vibrational freedom possessed by the colliding molecules. Quantum yields decline to a limiting value as the 6¹1¹ state is depopulated.

KEYWORDS and PACS

Keywords

BENZENE, EXCITATION, VAKPORS, VIBRATIONAL STATES, ENERGY−LEVEL TRANSITIONS, FLUORESCENCE, EXCITED STATES, PHOTOCHEMISTRY, CROSS SECTIONS, ABSORPTION SPECTRA, ROTATIONAL STATES, MOLECULE−MOLECULE COLLISIONS, PRESSURE DEPENDENCE

PACS

34.50.Fa

Electronic excitation and ionization of atoms (including beam-foil excitation and ionization)
33.50.Dq

Fluorescence and phosphorescence spectra
82.50.-m

Photochemistry