Search

The optical spectrum of jet-cooled Ge[sub 2] has been observed for the first time. Laser-induced fluorescence (LIF) and wavelength resolved emission spectra were recorded using the pulsed discharge technique with a tetramethylgermane precursor. Analysis of the spectra yielded the vibrational constants ω[sub e][sup ″]=287.9(47), ω[sub e]x[sub e][sup ″]=0.81(55), ω[sub e]y[sub e][sup ″]=0.0037(18), ω[sub e][sup ′]=189.0(15), ω[sub e]x[sub e][sup ′]=6.41(30), and T[sub e][sup ′]=20 610.8(16) cm-1. High-resolution rotationally resolved spectra of several bands of [sup 74]Ge[sub 2] show two strong P and R branches and two very weak Q branches. We have assigned the band system as a Hund’s case (c) Ω[sup ′]=1-Ω[sup ″]=1 transition from the ground [sup 3]Σ[sub g][sup -] state to a [sup 3]Σ[sub u][sup -] excited state. The bond lengths derived from the rotational constants are r[sub 0][sup ″]=2.3680(1) Å and r[sub e][sup ′]=2.5244(18) Å, an ∼0.16 Å increase on electronic excitation. Arguments are presented for assigning the transition to a σ[sub g][sup 2]π[sub u][sup 2]→σ[sub g][sup 2]π[sub u]π[sub g] electron promotion, although the observed increase in the bond length is much less than predicted by previous ab initio calculations. The absence of the 0[sub u][sup +]–0[sub g][sup +] component in the spectra has been attributed to an excited state predissociation. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The ground state vibrational energy levels of jet-cooled H[sub 2]CSi and D[sub 2]CSi have been studied by a combination of wavelength-resolved fluorescence and stimulated emission pumping (SEP) techniques. By taking advantage of the vibrational selection rules and Franck-Condon factors and selectively pumping upper state single vibronic levels, readily assignable low-resolution emission spectra were obtained. Higher resolution SEP spectra were recorded to give precise measurements of the vibrational band origins of many of the lower-lying vibrational levels. All of the vibrational frequencies, except for the Franck-Condon inactive CH asymmetric stretching mode, ν[sub 5], have been determined for both isotopomers. The CH[sub 2] rocking mode (ν[sub 6]) is found to have a very low 263 cm-1 frequency in the ground state. The spectra are complicated by unexpected activity in the out-of-plane bending vibration. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The ground state vibrational energy levels of jet-cooled SiCH and SiCD have been studied by a combination of laser-induced fluorescence and wavelength-resolved fluorescence techniques. The radicals were produced by a pulsed electric discharge at the exit of a supersonic expansion using tetramethylsilane or methyltrichlorosilane as the precursor. Emission spectra have been obtained by pumping both perpendicular and parallel (vibronically induced) bands, providing complementary information on the Si-C stretching and Si-C-H bending modes. Ground state energy levels up to 4000 cm-1 have been assigned and fitted using a vibrational Hamiltonian that incorporates Renner-Teller, spin-orbit, vibrational anharmonicity, and Fermi resonance interactions. The validity of the derived parameters has been tested using the isotope relations. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The A˜ [sup 2]Σ[sup +]-X˜ [sup 2]Π[sub i] electronic transition of jet-cooled germanium methylidyne has been recorded in the 730-555 nm region by laser-induced fluorescence techniques. The radical was produced in a pulsed electric discharge using tetramethylgermane as the precursor. The band system consists of perpendicular and vibronically induced parallel bands with upper state frequencies of ν[sub 2][sup ′]=638/497 cm[sup -1] and ν[sub 3][sup ′]=990/952 cm[sup -1] for GeCH/GeCD. The [sup 2]Σ[sup +]-[sup 2]Π[sub 3/2] components of the 0[sub 0][sup 0] bands of GeCH and GeCD and the 2[sub 0][sup 1] band of GeCH have been recorded with sufficient resolution to assign the transitions of the [sup 70]Ge, [sup 72]Ge, [sup 74]Ge, and [sup 76]Ge isotopomers. The rotational constants of the various hydrogen and germanium isotopomers were used to derive the following molecular structures: r[sub 0][sup ″](Ge-C)=1.775 79(21) Å, r[sub 0][sup ″](C-H)=1.0673(12) Å, r[sub 0][sup ′](Ge-C)=1.673 66(8) Å, and r[sub 0][sup ′](C-H)=1.0589(5) Å. The ground state germanium-carbon bond length is typical for a Ge=C double bond, but in the excited state it corresponds to a triple bond. This is a consequence of promotion of an electron from a nonbonding σ orbital to a π bonding orbital to form the ...σ[sup 1]π[sup 4]([sup 2]Σ[sup +]) excited state. In this study we provide the first experimental value for the length of the germanium-carbon triple bond. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The A˜ [sup 2]Σ[sup +]-X˜ [sup 2]Π[sub i] transition of jet-cooled silicon methylidyne, SiCH, has been recorded by laser-induced fluorescence in the 850-600 nm region. The radical was produced in an electric discharge using tetramethylsilane as the precursor. Fifteen cold bands of SiCH and 16 bands of SiCD have been assigned vibrationally, giving the upper state frequencies as v[sub 2][sup ′]=715/558 cm[sup -1] and v[sub 3][sup ′]=1168/1127 cm[sup -1] for SiCH/SiCD. Rotational analysis of the 0[sub 0][sup 0] and 3[sub 0][sup 3] bands for each isotopomer has given the following molecular structures: r[sub 0][sup ″](Si-C)=1.692 52(8), r[sub 0][sup ″](C-H)=1.0677(4), r[sub 0][sup ′](Si-C)=1.6118(1), and r[sub 0][sup ′](C-H)=1.0625(5) Å. The silicon-carbon bond length in the X˜ [sup 2]Π ground state of SiCH (electron configuration ...σ[sup 2]π[sup 3]) is typical for a Si=C double bond; in the A˜ [sup 2]Σ[sup +] excited state (...σ[sup 1]π[sup 4]) it corresponds to a triple bond. This work provides the first experimental measurement of the length of the carbon-silicon triple bond. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Growth of ordered perylene thin films on the Ag(110) surface has been investigated with scanning tunneling microscope. By saturating the surface with a monolayer of perylene molecules, two kinds of ordered structures are simultaneously formed with flat-lying perylene molecules on the Ag(110) surface, in which one is commensurate relative to the Ag substrate with a periodicity of (Multiple line equation(s) cannot be represented in ASCII text) while the other is commensurate with a periodicity of (Multiple line equation(s) cannot be represented in ASCII text). There is one molecule within the former unit cell with a surface coverage of 0.1 molecule per Ag atom, while there are two molecules within the latter unit cell, which gives a slightly lower surface coverage of 0.091 molecule per Ag atom. Ab initio calculations have been carried out to identify the adsorption geometry and bonding sites. [ABSTRACT FROM AUTHOR]

The structure of perylene adsorbed on Ru(0001) surface has been studied by ultraviolet photoemission spectroscopy (UPS) and low-energy electron diffraction. An ordered p(4×4) structure is observed from a monolayer (about 4 Å thickness) of the perylene on Ru(0001) surface. UPS measurements show the molecular features, from the perylene multiplayer, between 2 and 10 eV below the Fermi level. Angle-resolved ultraviolet photoemission spectroscopy measurements suggest that the perylene molecular plane is parallel to the substrate. Temperature dependent UPS measurements show that the perylene multilayer is stable on Ru(0001) surface up to 125 °C. The desorption of the multilayer and the decomposition of the monolayer are observed above 125 °C. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Photofragment NO[sup +] excitation spectrum of N[sub 2]O[sup +] ions has been studied in the wavelength range of 278–328 nm, where the parent N[sub 2]O[sup +] ions were state-selectively prepared at the X [sup 2]Π[sub 1/2,3/2](000) levels by [3+1] multi-photon ionization of jet-cooled N[sub 2]O molecules at 360.55 nm. The spectrum was attributed completely to the A [sup 2]Σ[sup +]←X [sup 2]Π[sub 3/2,1/2](000) electronic transition of N[sub 2]O[sup +]. Totally 47 vibronic bands associated to 24 vibrational levels of the A [sup 2]Σ[sup +] state were identified in the present work, most of which were observed for the first time. The sufficient spectroscopic data made it possible to investigate the Fermi-resonance between the ν[sub 1] and ν[sub 2] vibrational modes at the A [sup 2]Σ[sup +] state. Based on the assignment, the spectral constants of the A [sup 2]Σ[sup +] state, such as vibrational frequencies, anharmonic constants, and Fermi interaction constant, were determined with relatively high reliability and precision. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]