D. E. Tevault

Matrix isolation and laser diagnostic studies of catalytic oxidation of H2 and D2 on platinum

The reaction of hydrogen (or deuterium) and oxygen on pure polycrystalline platinum surfaces has been investigated in the 10−5 to 10−6 Torr range using the matrix isolation and laser‐induced fluorescence techniques. Water, formed with a 1.1±0.2 kcal/mole activation energy, was the only product detected by infrared spectroscopy at catalyst temperatures between 150 and 700 °C. Laser‐induced fluorescence experiments were used to observe the production of HO radicals both in argon matrices and in the gas phase. HO production was found to have an activation energy of 31±1 kcal/mole and could only be detected escaping from the surface at catalyst temperatures above 500 °C. The dependence of H2O and HO radical production on the partial pressures of H2 and O2 has been made. Reaction mechanisms are discussed in relation to other studies of the oxidation of hydrogen on single crystal and polycrystalline platinum surfaces.

Surface-enhanced Raman spectra of benzene and benzene-d6 on vapor-deposited sodium

Abstract Enhanced Raman spectra have been observed from small amounts of benzene and benzene-d6 adsorbed on vapor-deposited sodium surfaces held at 15 K. Many lines were observed which can be assigned to normally Raman-active benzene fundamentals as well as some that are normally forbidden in D6h symmetry.

Matrix reactions of copper atoms and ozone molecules. Infrared spectrum of CuO

The matrix reactions of copper atoms with ozone have been studied by infrared spectroscopy. Two products were found in the initial deposit: CuO3, which has a strong absorption at 802.3 cm−1, and CuO, which has its main feature, corresponding to the 63Cu16O isotopic species, at 628.0 cm−1 in solid argon. Copper atom reactions with oxygen‐18‐enriched ozone samples were used to obtain species identifications. The CuO3 absorption was very similar in frequency and isotopic splitting behavior to alkali and alkaline earth metal ozonide species previously studied in matrices. The CuO frequency is in good agreement with gas phase measurements which put the ground state CuO vibrational fundamental at 631.3 cm−1. Temperature cycling of the Cu–O3 matrices leads to CuO4 formation by the secondary reaction of CuO with unreacted ozone.

Matrix reactions of chlorine atoms with NO2 molecules

Matrix reactions of chlorine atoms with NO2 molecules diluted in argon yielded Cl–N bonded nitryl chloride ClNO2 as well as the Cl–O bonded isomer nitrosyl hypochlorite ClONO. Infrared absorptions at 1714.1, 855.6, 398.0, and 390.4 cm−1 were assigned to the ClONO species, which was shown from nitrogen‐15 and oxygen‐18 isotopic studies to be comprised of two weakly coupled diatomic radicals ClO and NO. Infrared spectroscopic evidence also suggested the presence of a third isomer OClNO which is produced by the insertion of a chlorine atom into an N–O bond of NO2 as well as by the direct maxtrix combination of ClO and NO radicals. The photolytic behavior of the ClONO species indicates that it undergoes intramolecular rearrangement, in the argon matrix cage, to produce the more stable ClNO2 form via a two‐step process which involves the OClNO molecule as an intermediate.

Chemiluminescent reactions of sulfur atoms and oxygen atoms in solid argon matrices. SO chemiluminescence

When dilute argon matrices containing H2S+O3, OCS+O3 and H2S+NO2 molecules are exposed to ultraviolet radiation and subsequently allowed to warm from 8 to ∼20°K, several intense visible emissions with extensive vibrational structure appear. Besides those emissions of O2, S2, and SO2, two new luminescent systems are evident. Extensive oxygen‐18 and deuterium isotopic studies demonstrated the absence of hydrogen and the presence of a single oxygen atom in the emitting species of both systems, while matrix concentration studies established that the excited state species was an intermediate in SO2 formation, presumably molecular SO. The more intense of the two systems is located between 490–870 nm and contains up to ten members. The low values calculated for T0=22 543 cm−1 and ωe″=1130.7 cm−1 suggest that this transition is most likely SO (c1Σ−→ a 1Δ). A second, weaker emission system of SO with approximately eight members was found between 385–600 nm. T0 for this latter system was estimated at 28 400±1150 cm...

Surface‐enhanced Raman scattering from vapor‐deposited copper, silver, and gold. Excitation profiles and temperature dependence

Surface‐enhanced Raman spectra (SERS) of pyridine adsorbed on copper, silver, and gold films vapor deposited on low temperature substrates are reported. Similar spectra were also obtained on a sputter‐cleaned silver single crystal. Excitation spectra (450–750 nm) for all three metals revealed an overall increase in SERS activity at longer wavelengths, the relative increase being greater for copper and gold than silver. A broad excitation maximum near 2 eV was observed for the 1006 cm−1 pyridine SERS signal on silver. A lesser‐defined maximum was revealed for copper in the same general vicinity (1.7–2.0 eV) while a broad onset extending below 1.7 eV was observed for gold. Temperature studies (15–300 K) indicate that the observed SERS originate from molecular pyridine chemisorbed to the metal surfaces. In the cases of copper and gold, SERS were also observed from samples maintained at room temperature in vacuum. The intensities of the SERS signals were proportional to incident (cw) laser power at low power ...

Laser‐induced emission spectrum of CuO2 in argon matrices

When argon matrices containing atomic Cu and O2 or O3 molecules at 10 K are excited with the blue laser lines of a krypton ion laser, several electronic emissions with extensive vibrational structure are observed. These were characterized as CuO2 emissions by the use of oxygen‐18 isotopic enrichment experiments where each member is split into a triplet, thereby indicating a CuO2 molecule with equivalent oxygen atoms. A second progression observed only when Cu atoms were deposited with argon–ozone samples is tentatively attributed to a resonance Raman progression of the Cu2O molecule. No emissions from CuO have been observed in these experiments.

Ozone and oxygen atom reactions with dimethylsulfide and methanethiol in argon matrices

Ground state oxygen atoms, generated by visible photolysis of ozone, have been reacted with CH3SCH3 and CH3SH in argon matrices. For CH3SCH3, a stepwise addition to form DMSO and dimethylsulfone was observed. Methanethiol reactions with O atoms were more complex, leading to production of CH3SOH, CH3OSH, CH3S(O)H, and possibly CH3–SO2–H. These results are compared to the O+H2S reaction. The matrix results are also compared to gas phase studies where more extensive fragmentation has been observed, and inferences are drawn concerning the relative matrix deactivation rates of the highly energetic sulfide–oxygen‐atom precursor complex.

Catalytic intermediates in the Ag–O2 system. Evidence for a nonsymmetric AgO2 molecule

Matrix isolated infrared spectra of AgO2 in Ar matrices is presented and a normal coordinate analysis of AgO2 is performed. (AIP)

Matrix reactions of ozone and oxygen atoms with hydrogen iodide. HOI formation

Oxygen atoms and ozone react with hydrogen iodide in dilute nitrogen and argon matrices at 8°K to produce new infrared absorptions at 3597, 1103, and 575 cm−1 which are attributed to the HOI intermediate species hypoiodous acid. The observed oxygen‐18 and deuterium isotopic frequencies and associated band assignments identified isolated H–O and O–I stretching modes which defined the H–O–I structural arrangement. Partially enriched oxygen‐18 and deuterium isotopic experiments confirmed the fact that the product contains one oxygen and one hydrogen atom per molecule. The vibrational spectrum of HOI is analogous to those of the other hypohalous acids.