Heavy hydrides: H{sub 2}Te ultraviolet photochemistry
- Department of Chemistry, University of Southern California, Los Angeles, California 90089 (United States)
The room-temperature ultraviolet absorption spectrum of H{sub 2}Te has been recorded. Unlike other group-6 hydrides, it displays a long-wavelength tail that extends to 400 nm. Dissociation dynamics have been examined at photolysis wavelengths of 266 nm (which lies in the main absorption feature) and 355 nm (which lies in the long-wavelength tail) by using high-n Rydberg time-of-flight spectroscopy to obtain center-of-mass translational energy distributions for the channels that yield H atoms. Photodissociation at 355 nm yields TeH({sup 2}{pi}{sub 1/2}) selectively relative to the TeH({sup 2}{pi}{sub 3/2}) ground state. This is attributed to the role of the 3A{sup '} state, which has a shallow well at large R{sub H-TeH} and correlates to H+TeH({sup 2}{pi}{sub 1/2}). Note that the {sup 2}{pi}{sub 1/2} state is analogous to the {sup 2}P{sub 1/2} spin-orbit excited state of atomic iodine, which is isoelectronic with TeH. The 3A{sup '} state is crossed at large R only by 2A{sup ''}, with which it does not interact. The character of 3A{sup '} at large R is influenced by a strong spin-orbit interaction in the TeH product. Namely, {sup 2}{pi}{sub 1/2} has a higher degree of spherical symmetry than does {sup 2}{pi}{sub 3/2} (recall that I({sup 2}P{sub 1/2}) is spherically symmetric), and consequently {sup 2}{pi}{sub 1/2} is not inclined to form either strongly bonding or antibonding orbitals with the H atom. The 3A{sup '}<-X transition dipole moment dominates in the long-wavelength region and increases with R. Structure observed in the absorption spectrum in the 380-400 nm region is attributed to vibrations on 3A{sup '}. The main absorption feature that is peaked at {approx}240 nm might arise from several excited surfaces. On the basis of the high degree of laboratory system spatial anisotropy of the fragments from 266 nm photolysis, as well as high-level theoretical studies, the main contribution is believed to be due to the 4A{sup ''} surface. The 4A{sup ''}<-X transition dipole moment dominates in the Franck-Condon region, and its polarization is in accord with the experimental observations. An extensive secondary photolysis (i.e., of nascent TeH) is observed at 266 and 355 nm, and the corresponding spectral features are assigned. Analyses of the c.m. translational energy distributions yield bond dissociation energies D{sub 0}. For H{sub 2}Te and TeH, these are 65.0{+-}0.1 and 63.8{+-}0.4 kcal/mol, respectively, in good agreement with predictions that use high-level relativistic theory.
- OSTI ID:
- 20723034
- Journal Information:
- Journal of Chemical Physics, Vol. 123, Issue 8; Other Information: DOI: 10.1063/1.2008261; (c) 2005 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA); ISSN 0021-9606
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ABSORPTION
ABSORPTION SPECTRA
CENTER-OF-MASS SYSTEM
DIPOLE MOMENTS
DISSOCIATION
DISSOCIATION ENERGY
ENERGY SPECTRA
GROUND STATES
L-S COUPLING
PHOTOCHEMISTRY
PHOTOLYSIS
PHOTON-MOLECULE COLLISIONS
REACTION KINETICS
RYDBERG STATES
TELLURIUM HYDRIDES
TIME-OF-FLIGHT METHOD
ULTRAVIOLET RADIATION
VIBRATIONAL STATES