High resolution emission spectroscopy of the AП-XΣ (red) system of CN

The emission spectra of the A²П-X²Σ⁺ (red) system of ¹²C¹⁴N have been reinvestigated in the 3500-22 000 cm⁻¹ region at high resolution using a Fourier transform spectrometer. In total, spectra of 63 bands involving vibrational levels up to v′ = 22 of the A²П state and v″ = 12 of the X²Σ⁺ ground state have been measured and rotationally analyzed providing an improved set of spectroscopic constants. The present measurements of the Δv = −2 sequence bands of ¹²C¹⁴N and those of ¹³C¹⁴N from Ram et al. (2010) [36] allow for a much improved identification of these two isotopologues in the near infrared spectra of carbon stars.     

Fundamental studies of the cluster ion bombardment of water ice

The fundamental sputtering properties of water ice are of interest for molecular depth profiling of biological samples in their native environment. We report on a method of studying amorphous water ice films of precise thicknesses in which pure water vapor is condensed onto a pre-cooled, silver-coated quartz crystal microbalance (QCM). This scheme allows for the determination of water ice sputter yields for any primary projectile as well as providing a means for studying escape depths of atoms and molecules beneath the deposited water ice layer. Specifically, we find a removal of approximately 2500 water molecule equivalents/20 keV C₆₀⁺ projectile with an underlying silver ion escape depth of 7.0 Å.     

On the cΠ (v = 0) state of carbon monoxide

A full analysis of the near infrared c³Π-b³Σ⁺ (0-0) band is given and term values for both states determined. The c³Π (v = 0) state was jointly analysed with the perturbing k³Π (v = 2) state and data from the c³Π-X¹Σ⁺ (0-0) transition and 3A band system were included. It is shown that the available data are consistent with the c³Π (v = 0) state having near Hund’s case b coupling with a spin-orbit constant of A = 0.45 ± 0.02 cm⁻¹, a homogeneous perturbation with the k³Π (v = 2) state, and Λ-type doubling arising predominantly from its interaction with the j³Σ⁺ state. A discrepancy with a more recent report of the 3A band system is identified and discussed. The perturbed b³Σ⁺ state term values are consistent with a previously reported five state interaction model.     

New spectroscopic investigations of the fourth-positive (AΠ → XΣ) system bands in the CO molecule

The present work puts forward the results of the recordings carried out under high resolution by conventional, photographic spectroscopy and modern analysis of thirteen bands with v′ = 7-12 and v″ = 16-24 of the fourth-positive (A¹Π → X¹Σ⁺) band system. The current investigations include the region of the observed ¹³C¹⁶O molecule spectrum, much greater now than before. Especially, new transitions connected with not hitherto observed v′ = 12 vibrational level of the A¹Π state, were recorded and studied. Moreover, the region of perturbations observed in the upper state of the fourth-positive system was significantly enlarged. The observed perturbations were confronted with those predicted from theoretical calculations.     

Time-resolved Fourier transform emission spectroscopy of AΠ-XΣ infrared transition of the CN radical

The A²Π-X²Σ⁺Δv = −3 bands of the ¹²C¹⁴N radical have been observed by time-resolved Fourier transform spectroscopy in the 1850-3100 cm⁻¹ region with a wavenumber resolution of 0.025 cm⁻¹. The radical was produced in a pulsed positive column discharge in a cyanogene and helium mixture. Seven bands of v = 0-3, 1-4, 2-5, 3-6, 4-7, 5-8, and 6-9 were analyzed to give the molecular constants of each state by least-squares fitting of 801 lines. The pulsed discharge was found to be efficient for production of CN in the excited A²Π state. The vibrational excitation temperature was determined to be 6680 ± 835 K and 6757 ± 534 K for the A²Π and X²Σ⁺ states, respectively. The population of the A²Π was found to be 4% of that of the X²Σ⁺ state in the time after turning off the discharge.     

Influence of massive projectile size and energy on secondary ion yields from organic surfaces

We investigated the influence of the projectile size and energy using Au_n^q+ clusters (5 < n < 400, 1 < q < 4) impacting on a glycine target with a 19q-34q keV energy range. We show that both CN⁻ fragment and Gly⁻ molecular ion yields are equivalent for projectiles with n > 9 and increase with the energy per projectile atoms. A maximum yield of 0.5 (50%) for both CN⁻ and Gly⁻ was obtained with the Au₄₀₀⁴⁺ projectile at 136 keV total energy. For Gly⁻, the yield enhancement is linear for Au_n when n > 5. Trends for the CN⁻ fragment are different. A nonlinear yield enhancement proportional to n³ is observed for Au_n when n < 9.     

Effect of surface steps on sputtering and surface defect formation: molecular-dynamics study of 5 keV Xe bombardment of Pt(1 1 1) at glancing incidence angles

Using molecular-dynamics simulation, we study sputtering and defect formation induced by 5 keV Xe⁺ ion impact on a Pt(1 1 1) surface at oblique and glancing incidence angles. Impact on a terrace produces yield maxima at ?=60-65° incidence angle towards the surface normal. Beyond 75-80°, no damage is produced due to projectile ion reflection. Impact on a dense-packed step, however, produces defects in sizeable numbers up to glancing incidence, ?=85°. The dependence of the yields on the incidence angle and distance of the impact point of the projectile to the step are discussed.     

Formation of Sim and SimCn clusters by C60 sputtering of Si

The secondary ion mass spectrum of silicon sputtered by high energy C₆₀⁺ ions in sputter equilibrium is found to be dominated by Si clusters and we report the relative yields of Si_m⁺ (1 ≤ m ≤ 15) and various Si_mC_n⁺ clusters (1 ≤ m ≤ 11 for n = 1; 1 ≤ m ≤ 6 for n = 2; 1 ≤ m ≤ 4 for n = 3). The yields of Si_m⁺ clusters up to Si₇⁺ are significant (between 0.1 and 0.6 of the Si⁺ yield) with even numbered clusters Si₄⁺ and Si₆⁺ having the highest probability of formation. The abundances of cluster ions between Si₈⁺ and Si₁₁⁺ are still significant (>1% relative to Si⁺) but drop by a factor of ∼100 between Si₁₁⁺ and Si₁₃⁺. The probability of formation of clusters Si₁₃⁺-Si₁₅⁺ is approximately constant at ∼5 × 10⁻⁴ relative to Si⁺ and rising a little for Si₁₅⁺, but clusters beyond Si₁₅ are not detected (Si_m≥16⁺/Si⁺ < 1 × 10⁻⁴). The probability of formation of Si_m⁺ and Si_mC_n⁺ clusters depends only very weakly on the C₆₀⁺ primary ion energy between 13.5 keV and 37.5 keV. The behaviour of Si_m⁺ and Si_mC_n⁺ cluster ions was also investigated for impacts onto a fresh Si surface to study the effects that saturation of the surface with C₆₀⁺ in reaching sputter equilibrium may have had on the measured abundances. By comparison, there are very minor amounts of pure Si_m⁺ clusters produced during C₆₀⁺ sputtering of silica (SiO₂) and various silicate minerals. The abundances for clusters heavier than Si₂⁺ are very small compared to the case where Si is the target.The data reported here suggest that Si_m⁺ and Si_mC_n⁺ cluster abundances may be consistent in a qualitative way with theoretical modelling by others which predicts each carbon atom to bind with 3-4 Si atoms in the sample. This experimental data may now be used to improve theoretical modelling.     

Carbon sputtering yield measurements at grazing incidence

In this investigation, carbon sputtering yields were measured experimentally at varying angles of incidence under Xe⁺ bombardment. The measurements were obtained by etching a coated quartz crystal microbalance (QCM) with a low energy ion beam. The material properties of the carbon targets were characterized with a scanning electron microscope (SEM) and Raman spectroscopy. C sputtering yields measured under Ar⁺ and Xe⁺ bombardment at normal incidence displayed satisfactory agreement with previously published data over an energy range of 200 eV-1 keV. For Xe⁺ ions, the dependence of the yields on angle of incidence θ was determined for 0° ≤ θ ≤ 80°. Over this range, an increase in C sputtering yield by a factor of 4.8 was observed, with the peak in yield occurring at 70°. This is a much higher variation compared to Xe⁺ → Mo yields under similar conditions, a difference that may be attributed to higher scattering of the incident particles transverse to the beam direction than in the case of Xe⁺ → C. In addition, the variation of the yields with θ was not strongly energy dependent. Trapping of Xe in the surface was observed, in contrast to observations using the QCM technique with metallic target materials. Finally, target surface roughness was characterized using atomic force microscope measurements to distinguish between the effects of local and overall angle of incidence of the target.     

Sputtering yields of PMMA films bombarded by keV C60 ions

A quartz crystal microbalance (QCM) has been used to determine total-mass sputtering yields of PMMA films by 1-16 keV C₆₀^+,2+ ion beams. Quantitative sputtering yields for PMMA are presented as mass loss per incident ion Y_m. Mass-lost rate QCM data show that a 13 keV C₆₀ cluster leads to emission equivalent to 800 PMMA molecules per ion. The power law obtained for the increase in sputtering yield with primary ion energy is in good agreement those predicted by “thermal spike” regime and MD models, when crater sizes are used to estimate sputtering.     

Investigation of four carbon monoxide isotopomers in natural abundance by laser-induced fluorescence in a supersonic jet

The four carbon monoxide (CO) isotopomers ¹²C¹⁶O, ¹³C¹⁶O, ¹²C¹⁸O and ¹²C¹⁷O have been detected simultaneously in a CO gas sample of natural isotopic abundance by measuring rovibronic excitation spectra of six vibronic bands in the Fourth Positive System. The CO sample was flow cooled by adiabatic expansion in a pulsed supersonic jet. The rovibronic excitation spectra were obtained using a novel pulsed laser source (pulse duration ∼25 ns, spectral bandwidth ∼5 GHz) continuously tunable in the 139-155 nm vacuum ultraviolet wavelength region for excitation and recording the total fluorescence. In the present paper we report on the spectroscopic results obtained, including transition wavelengths of three forbidden rovibronic bands (e³Σ⁻ −  X¹Σ⁺(1, 0), d³Δ  − X¹Σ⁺(5, 0), a′³Σ⁺ −  X¹Σ⁺(14, 0)) of ¹²C¹⁶O and band origins of six rovibronic bands (A¹Π(v′ = 0-5) −  X¹Σ⁺(v″ = 0)) of the rare isotopomer ¹²C¹⁷O, and on the experimental conditions facilitating the high sensitivity of the measurements. The exceptional sensitivity demonstrated by the results has been achieved by fine tuning experimental conditions including the conditions in the supersonic expansion, the jet pulse duration and the laser pulse timing.     

Substrate effects on the analysis of biomolecular layers using Au, Au3 and C60 bombardments

Effects of platinum silicon, graphite and PET substrates on the secondary ion yield of sub-monolayer and multilayer samples of Cyclosporin A following 20 keV Au⁺, Au₃⁺and C₆₀⁺ impacts have been investigated. The obtained results of sub-monolayer samples show that platinum enhances the yield of the pseudo-molecular ion following Au⁺ and Au₃⁺ impacts due to the high density of the substrate that enables the energy of the primary ions to be deposited near the surface. C₆₀⁺ impacts on sub-monolayer samples are less effective, but there is an enhancement on PET substrates. Impacts of 20 keV Au⁺ and Au₃⁺ are not very efficient on multilayer samples. 20 keV C₆₀⁺ impacts enhance the yields significantly, especially for the relatively high molecular weight [M+H]⁺ ion.     

Desorption of cluster ions from adsorbed methane under cryogenic condition by low-energy ion irradiation

We have investigated ion desorption from adsorbed methane following keV He⁺ ion irradiation. The thickness of the adsorbed layer was precisely controlled. For mono-layered methane, only monomer ions (CH_x⁺) were desorbed by 1 keV He⁺ ion irradiation. On the other hand, a large number of cluster ions (C_nH_x⁺) up to n = 20 were desorbed from multi-layered film. Among cluster ions, molecular ions with CC bonds were found, which indicates that chemical bonds are newly formed by ion irradiation. Based on the results for thickness dependences of the mass spectral patterns, it was elucidated that the monomer ions are desorbed from the top surface layer through single electron excitation. While the cluster ions are formed mainly in the inside of the layers along the nuclear track due to the high-density electronic excitation, which is produced by nuclear collision between incident He⁺ ions and frozen molecules.     

Organic SIMS with single massive gold projectile: Ion yield enhancement by silver metallization

The yield of CN from glycine rises from one CN per projectile impact to two when the sample is covered with a nominally 1 nm thick layer of silver. These yields were obtained for bombardment with Au₄₀₀⁴⁺ projectile with 136 keV impact energy. A multitude of CN-based clusters, e.g. Ag_xO_y(CN)_z are produced concurrently. As a result, a total of three CN-based secondary ions are generated per projectile impact. The exceptionally high yield for CN is of interest for biological SIMS.     

Spectroscopy of AlO: Combined analysis of the AΠi → XΣ and BΣ → XΣ transitions

A combined analysis of the A²Π_i → X²Σ⁺ and B²Σ⁺ → X²Σ⁺ band systems of AlO, involving 21,500 line assignments, has been performed. The analysis indicates that the previously reported γ values of the B²Σ⁺ state are questionable. The present analysis shows that γ(B²Σ⁺) ≈ 0.014 cm⁻¹, essentially independent of the vibrational level. The positive sign is consistent with second order interaction with the higher-lying C²Π_r and lower-lying A²Π_i states. It also appears that many of the previously reported γ and γ_D values of X²Σ⁺ (v > 0) are doubtful. In fact, γ(X²Σ⁺) is observed to become increasingly negative for v″ > 1, due to second order interaction with the low-lying A²Π_i state. The present results are based on models where the hyperfine structure of the ²Σ⁺ states has been taken into account explicitly. Intensity patterns of the branches of the B²Σ⁺ → X²Σ⁺ system have been shown to be influenced by the case bβ_S coupling in the ground state v = 0,1 levels. This gives rise to intensity differences of around 10 percent in the R₁/R₂ and P₁/P₂ doublet components. The synthesized intensity patterns are fully in accord with the F₁/F₂ assignments of the present work.     

Positive secondary Ion emission from Si1−xGex bombarded by O2

The positive secondary ion yields of B⁺ (dopant), Si⁺ and Ge⁺ were measured for Si_1−xGe_x (0 ≤ x ≤ 1) sputtered by 5.5 keV ¹⁶O₂⁺ and ¹⁸O₂⁺. It is found that the useful yields of Ge⁺ and B⁺ suddenly drop by one order of magnitude by varying the elemental composition x from 0.9 to 1 (pure Ge). In order to clarify the role of oxygen located near surface regions, we determined the depth profiles of ¹⁸O by nuclear resonant reaction analysis (NRA: ¹⁸O(p,α)¹⁵N) and medium energy ion scattering (MEIS) spectrometry. Based on the useful yields of B⁺, Si⁺ and Ge⁺ dependent on x together with the elemental depth profiles determined by NRA and MEIS, we propose a probable surface structure formed by 5.5 keV O₂⁺ irradiation.     

Cavity ring down absorption spectroscopy of the BΣ-XΣ transition of YO

The absorption spectrum of the (2, 0) and (2, 1) bands of the B²Σ⁺-X²Σ⁺ transition of YO between 442 and 478 nm were recorded using laser vaporization/reaction with free-jet expansion and cavity ring down laser absorption spectroscopy. Local rotational perturbations have been found for both spin components of the v = 2 level of the B²Σ⁺ state. The observed perturbations could be ascribed to a degenerate perturbing state interacting with the B²Σ⁺ state. Least-squares fit of the observed upper state term values yielded molecular constants for the v = 2 level of the B²Σ⁺ state and the perturbing ²Π state. Earlier ab initio calculations [J. Chem. Phys. 89 (1988) 2160] indicated that the C²Π state is nearby, it is plausible that the C²Π state is the perturbing state.     

Elastic constants of solids and fluids with initial pressure via a unified approach based on equations-of-state

The second and third-order Brugger elastic constants are obtained for liquids and ideal gases having an initial hydrostatic pressure p₁. For liquids the second-order elastic constants are C₁₁ = A + p₁, C₁₂ = A − p₁, and the third-order constants are C₁₁₁ = −(B + 5A + 3p₁), C₁₁₂ = −(B + A − p₁), and C₁₂₃ = A − B − p₁, where A and B are the Beyer expansion coefficients in the liquid equation of state. For ideal gases the second-order constants are C₁₁ = p₁γ + p₁, C₁₂ = p₁γ − p₁, and the third-order constants are C₁₁₁ = −p₁(γ² + 4γ + 3), C₁₁₂ = −p₁(γ² − 1), and C₁₂₃ = −p₁ (γ² − 2γ + 1), where γ is the ratio of specific heats. The inequality of C₁₁ and C₁₂ results in a nonzero shear constant C₄₄ = (1/2)(C₁₁ − C₁₂) = p₁ for both liquids and gases. For water at standard temperature and pressure the ratio of terms p₁/A contributing to the second-order constants is approximately 4.3 × 10⁻⁵. For atmospheric gases the ratio of corresponding terms is approximately 0.7. Analytical expressions that include initial stresses are derived for the material ‘nonlinearity parameters’ associated with harmonic generation and acoustoelasticity for fluids and solids of arbitrary crystal symmetry. The expressions are used to validate the relationships for the elastic constants of fluids.     

New analysis of the Comet-Tail (AΠi − XΣ) system in the CO isotopic molecule

The emission spectra of the 0-2, 4-2, and 6-1 bands of the Comet-Tail (A²Π_i − X²Σ⁺) system in the ¹⁴C¹⁶O⁺ isotopic molecule, comprising nearly 600 lines, have been recorded and analyzed for the first time. The spectra have been photographed under high resolution by using conventional spectroscopy, and it was possible to separate and observe most of the lines of all the 12 branches of this transition. The reduction of the individual bands’ spectra has been performed by nonlinear least-squares procedure and by means of effective Hamiltonians of Brown et al. the rovibronic structure parameters have been obtained. The currently investigated bands of the Comet-Tail system and the earlier analyzed bands of the A − X and B − A systems in the ¹⁴C¹⁶O⁺ molecule have been merged together. The results of this global fit made it possible to derive a new set of the equilibrium molecular constants for the A and X states. Then the RKR potential curve parameters for both A and X states and Franck-Condon factors as well as r-centroids for the A − X transition have been calculated for the ¹⁴C¹⁶O⁺ molecule.