Scott A. Ekberg

Hindered rotation and site structure of methane trapped in rare gas solids

High resolution infrared absorption spectra have been recorded for the ν4 vibrational mode of CD4 trapped in solid argon and krypton. As with CH4, evidence for two dominant sites was found: one with a cubic close‐packed (CCP) environment and the other with a hexagonal close‐packed (HCP) environment. The fine structure for the CCP site resembles that for a tetrahedral molecule rotating in an octahedral field: singlet peaks for P(1), Q(1), and R(0), and a doublet for R(1). The fine structure for the HCP site is more complex and is not assigned to specific rotational transitions. By high temperature annealing it was possible to eliminate the HCP site completely with increase in concentration of the more stable CCP site. The slow relaxation of nuclear spin found for CH4, from an F state (J=1) to an A state (J=0), was found to be two orders of magnitude faster for CD4.

Potential constants and structure of the UF5 monomer

Three infrared‐active UF stretching modes have been observed for UF5 isolated in argon and neon matrices. From the frequencies and their relative intensities the structure and UF force constants have been estimated. It is quite clear that the molecule has C4v symmetry, the axial bond has the same strength as the UF bonds in UF6, the radial bonds are somewhat weaker, and the axial–radial UF, UF′ angle is about 101°.

Orientational ordering and site structure of SiF4 trapped in rare gas solids

The infrared spectrum of the ν3 mode of SiF4 shows only one site with marked site‐symmetry splitting accompanied by pronounced (>95%) orientational ordering. The results indicate a site symmetry of C3v with the SiF4 molecule occupying a four‐atom substitutional site with a cubic‐close‐packed environment. In krypton and xenon matrices, however, SiF4 occupies a three‐atom substitutional site. The fact that SiF4 shows only one dominant site when present in argon matrices of UF6 indicates that one of the two UF6 sites has a local hexagonal close packed environment induced by short range stacking faults.

Temperature reversible IR spectral changes and site structure dynamics for SeF6 isolated in krypton matrices

High-resolution FTIR results for SeF6 trapped in a krypton matrix exhibit dramatic temperature reversible spectral changes for the complex v3 structure. The spectral changes are believed to result from dynamic exchange among low symmetry trapping sites on the infrared time scale to give an effective site symmetry change.

The use of single crystal rare gas lattices to study homogeneous lineshapes of impurities: SF6 in xenon

Abstract The IR absorption spectrum of SF6 in single crystal xenon has been studied as a function of temperature. Only one trapping site is stable in single crystal xenon and the v3 linewidth for this site is dominated by homogeneous broadening throughout the entire temperature range studied (14–160 K). The v3 linewidth shows an approximate eαT dependence which is inconsistent with either elastic phonon scattering or local phonon modes independently as the dominant dephasing mechanism. The results suggest that dephasing involves both site local and bulk phonon modes with the former dominating at low temperatures and the latter at higher temperatures.

Infrared spectra and structure of thin films of solid oxygen: A metastable phase

The infrared absorption spectra of thin films of solid oxygen prepared by vapor deposition is examined in detail. It is shown that at deposition temperatures between 8 and 11 K the film consists of a mixture of α‐O2 and a metastable phase we call m‐O2. The spectrum of CO in an O2 matrix is shown to be a good marker for the presence of m‐O2 and is informative concerning the structure of this metastable phase. Studies of mixtures of 18O2 and 16O2 indicate that the structure of m‐O2 is complex with four nonequivalent sites for O2 molecules and at least eight molecules per unit cell. The isotopic studies suggest the presence of weakly bound dimers as well as tetramers or higher multimers in m‐O2. It is shown that the presence of a few percent impurities such as nitrogen or argon allow the formation of and increase the stability of m‐O2 at higher temperatures. However, with or without impurities, at deposition temperatures below 8 K less m‐O2 is formed, and deposition at 5 K leads to no m‐O2 but only poorly cr...

Laser excitation of SF6 in low temperature matrices

Infrared spectra of SF6 in an Ar matrix at 10°K is reported. The spectrum was excited by CO2 laser.(AIP)

Vibrational spectrum and potential constants for S2F10

Abstract The i.r. and Raman spectra of S 2 F 10 vapor have been observed and new assignments have been made for several of the fundamental modes. In particular the band pumped in laser dissociation experiments [1] is an E 1 radial SF stretch rather than a B 2 axial SF stretch as earlier assigned [2, 3]. From matrix-isolation i.r. spectra some of the 32 S 32 S→ 32 S 34 S isotope shifts have been observed. From the results, with the aid of literature data on SF 6 to make judicious constraints, a general quadratic force field for S 2 F 10 has been estimated; the SF bonds are somewhat weaker than those of SF 6 .

Photoinduced reaction of UF6 with SiH4 in a low temperature SiH4 matrix

Results are reported that contradict the interpretation of Catalano et al.2 for observing photoinduced reactions of UF6 with SiH4 in a low temperature SiH4 matrix. It was found that the reactions occur due to near uv irradiation in the UF6 A band (25 000–29 000 cm−1) rather than the 613 cm−1 ν3 absorption of UF6.(AIP)

Pulse expansion deposits and orientational ordering for low temperature matricesa)

Low temperature matrices of SF6 in xenon were prepared by pulsed expansion of premixed gas through a conical 0.5 mm orifice onto a cold window. Infrared polarization studies were made of the orientational ordering exhibited by the ν3 mode at ∼933 cm−1. The orientational ordering was similar to that of big pulse deposits at 40 K and below but less for 50 K deposits. The pronounced polarization observed suggests an anomaly in the refractive index of the matrices prepared by this technique. For deposits at 50 K, aggregation is found to be negligible for pulsed expansion while it is significant for large pulse deposits, and even greater for the slow‐spray‐on technique.