William G. Golden

A method for measuring infrared reflection—Absorption spectra of molecules adsorbed on low-area surfaces at monolayer and submonolayer concentrations

Instrumentation has now been developed for the measurement of infrared reflection-absorption spectra (IRRAS); this is a very sensitive technique which can easily detect the vibrational spectra of many adsorbates at submonolayer concentrations on low-area surfaces. Furthermore, being a photons-in photons-out technique, it is capable of being applied in the presence of adsorbant molecules in the gas phase at pressures in the range 10−11–102 Torr and with substrate temperatures ranging from 77 to 1200 K. These features of the technique make it ideally suited to the study of surface species present during actual catalytic reactions. Details of the design and operation of an IRRAS spectrometer are described.

Intensities of binary overtone and combination bands in the ir spectrum of CClF3

The intensities of the fundamental, binary overtone and binary combination bands in the ir spectrum of CClF3 have been measured. The intensities of the fundamentals have been interpreted in terms of a polar‐tensor model; those of the overtone and combination bands have been interpreted in terms of a model which ascribes all the intensity to mechanical anharmonicity and none to higher terms in the dipole–moment expansion in normal coordinates. It appears, from the success of this model, that the contributions from the second derivatives of the dipole moment to the binary overtone and combination bands are relatively unimportant in this molecule.

Intensities of binary overtones and combinations in the infrared spectrum of CF4

The intensities of the binary overtone and combination bands in the infrared spectrum of CF4 have been measured. The dipole strengths of the allowed two‐quantum transitions have been determined from the measured intensities and have been compared with the dipole strengths calculated from the anharmonic terms in the intramolecular potential‐energy function. The discrepancies between the observed and calculated dipole strengths have been used to estimate the second derivatives of the molecular dipole moment with respect to the dimensionless normal coordinates.

Infrared spectra of 14NO and 15NO on a low-area Pt surface at elevated temperatures

Abstract Infrared spectra of NO adsorbed on an annealed polycrystalline Pt surface have been measured at temperatures between 300 and 673 K and under pressures of gas-phase NO between 10 −3 and 1 Torr. The spectra show that the NO adsorbate is in equilibrium with the gas phase at elevated temperatures. A model based on strong vibrational coupling between NO molecules adsorbed on adjacent Pt atoms is proposed to explain the observed spectra.

Three-quantum transition probabilities in the ν3 manifold of SF6 and the assignment of the observed 3ν3 transition in the i.r. spectrum

Abstract A theoretical expression has been derived for the intensity of a three-vibrational-quantum electric-dipole transition and has been used to calculate the intensities of the transitions from the ground state to the two F 1 u components of 3ν 3 of SF 6 . The calculated intensity of 1.02 × 10 −2 km/mol is in reasonable agreement with the observed intensity of 4.8 × 10 −2 km/mol.

The infrared spectrum of an adsorbate formed from NH3 on polyerystalline Pt (111)

Abstract We have studied the infrared reflection-absorption spectrum of an adsorbate formed when an annealed polycrystalline Pt foil, presumably having a (111) surface structure, is exposed to ammonia gas at pressures in the range 0.1–10 torr. Isotopic substitution establishes that the adsorbate contains N 2 in addition to NH x species. There is also CN present in the adsorbate, presumably formed by reaction of nitrogen with carbon impurities on the surface.

3‐quantum transition probabilities in the ν3 manifold of UF6 and the assignment of 3ν3 in the observed infrared spectrum

Although there are two F1u components in 3ν3 of UF6 and transitions are allowed from the vibrational ground state to both, only a single band has been observed in the ir spectrum. These two states may be identified in a Cartesian representation of the normal coordinates as 3ν3x and 2ν3x+ν3y; on the basis of calculated intensities, the observed transition has been assigned to 3ν3x. The calculation of the dipole strengths required us to derive the octahedral splitting parameters G33 and T33 and these have been used to calculate the anharmonic splittings in the ν3 vibrational manifolds of 238UF6 and 235UF6.

Intensities of binary overtone and combination bands in the i.r. spectrum of NF3

Abstract The intensities of the binary overtone and combination bands in the i.r. spectrum of NF3 have been measured in the gas phase and in liquid—argon solution. The observed intensities have been interpreted in terms of a simple model which ascribes all the intensity of the binary overtones and combinations to anharmonic coupling with the fundamentals; i.e., a model in which the second derivatives of the dipole moment with respect to the normal coordinates are assumed to be zero. The agreement between the observed intensities and the calculated ones is extremely good for the bending modes but less satisfactory for the stretching modes. The use of a polar-tensor model to predict the intensities of the vibrational fundamentals is also explored.