Spectra and emission lifetimes of H2CS(Ã 1A2)

Fluorescence spectra and lifetimes of single vibronic levels of the first excited singlet state of H₂CS have been measured under effusive flow conditions. Fluorescence lifetimes of the single vibronic levels decrease from 140±3 μs (0°) to 68 μs(3¹4¹5¹) with increasing excitation energies. The promoting vibrational modes for the non-radiative transition are considered to be the out-of-plane bending (ν₄) and the asymmetric rocking (ν₆) modes rather than the asymmetric stretching mode (ν₅).     

Low temperature fluorescence studies of the deactivation of the bend—stretch manifold of CO2

Laser fluorescence has been used to measure rate constants for the vibrational of the bend—stretch manifold of CO₂ between 300 and 170 K. The technique employed a pulsed chemical CO laser to produce vibrationally excited CO. This was used in a collisional pumping scheme designed to deposit an excess of vibrational energy in the bend—stretch manifold of CO₂. The deactivation of this vibrational manifold has been studied using the following collisional partners: CO₂, Ar, Xe, N₂ and H₂. Our results are compared with the limited amount of other low temperature data which have been published and with data obtained using a shock tube in the temperature range of about 1000 to 400 K. The present low temperature and the published high temperature results extrapolate together smoothly and clearly show the large deviations from Landau—Teller behaviour which occur at low temperatures.     

Inversion Vibrational Energy Levels of PH3+(X2A2") Calculated by a New Two-dimension Variational Method

A new 2-D variational method is proposed to calculate the vibrational energy levels of the symmetric P-H stretching vibration (v1) and the symmetric umbrella vibration (inversion vibration) (v2) of PH₃⁺(X²A₂") that has the tunneling effect. Because the symmetric internal Cartesian coordinates were employed in the calculations, the kinetic energy operator is very simple and the inversion vibrational mode is well characterized. In comparison with the often used 1-D model to calculate the inversion vibrational energy levels, this 2-D method does not require an assumption of reduced mass, and the interactions between the v1 and v2 vibrational modes are taken into consideration. The calculated vibrational energy levels of PH₃⁺ are the first reported 2-D calculation, and the average deviation to the experimental data is less than 3 cm^-1 for the first seven inversion vibrational energy levels. This method has also been applied to calculate the vibrational energy levels of NH₃. The application to NH₃ is less successful, which shows some limitations of the method compared with a full dimension computation.     

Semiclassical calculation of rate costants for energy transfer between the asymmetric stretch mode of CO2 and N2

By using a semiclassical method for energy transfer in polyatomic molecules we have calculated 21 rate constants for vibration-vibration transitions between the asymmetric stretch mode of CO₂ and the vibrational mode of N₂ in the temperature range 50–700 K.     

Estimation of 14CO2 amount in the atmosphere

Carbon from fossil CO₂ emissions, without a significant presence of ¹⁴C, causes dilution of ¹⁴C in the carbon isotopic mixture (Suess effect). Reported ¹⁴C activities are usually connected to radiocarbon amount in the carbon isotopic mixture. Our paper is aimed on estimation of ¹⁴C/¹⁴CO₂ amount in the atmosphere (and its trend), utilizing calculation of a ¹⁴C activity concentration. A parameter connected only with a ¹⁴C quantity in the volume or mass unit of air is not influenced by a fossil carbon amount. Such a “robust” parameter can be influenced only by processes connected with ¹⁴C emissions/depositions.     

Infrared Photodissociation Spectroscopic and Theoretical Study of [Co(CO2)n]+ Clusters

The mass-selected infrared photodissociation (IRPD) spectroscopy was utilized to investigate the interactions of cationic cobalt with carbon dioxide molecules. Quantum chemical calculations were performed on the [Co(CO₂)_n]⁺ clusters to identify the structures of the low-lying isomers and to assign the observed spectral features. All the [Co(CO₂)_n]⁺(n=2-6) clusters studied here show resonances near the CO₂ asymmetric stretch of free CO₂ molecule. Experimental and calculated results indicate that the CO₂ molecules are weakly bound to the Co⁺ cations in an end-on con guration via a charge-quadrupole electrostatic interaction. The present IRPD spectra of [Co(CO₂)_n]⁺ clusters have been compared to those of Ar-tagged species ([Co(CO₂)_n]⁺-Ar), which would provide insights into the tagging effect of rare gas on the weakly-bounded clusters.     

A photoacoustic study of the collisional deactivation of CO2 by N2, CO and O2 between 160 and 375 K

A photoacoustic method is used under such experimental conditions that the (01¹0) level of CO₂ gas is not in equilibrium with the other vibrational levels. The rate constants κ′₁₀ characterizing the CO₂ (01¹0) collisional deactivation by N₂, CO and O₂ are measured directly.     

Vibrational radiative lifetimes in H2Se and HCS−

Vibrational dipole matrix elements and radiative transition probabilities for H₂Se and HCS⁻ have been evaluated from theoretical three-dimensional electric dipole moment and potential energy functions. The radiative lifetimes of the (v=1,J=0) levels of HCS⁻ have been calculated to be 3.5 ms (CH stretch), 172 ms (HCS bend) and 785 ms (CS stretch), and in H₂Se to be 122 ms (symmetric stretch), 1045 ms (bend) and 101 ms (asymmetric stretch). The lifetimes of higher vibrational states with no extensive mode-mixing decrease with increasing vibrational quantum number and vary in a mode-specific way.     

An EELS study of CO2 and CO3 adsorbed on oxygen covered Ag(110)

The vibrational spectra of CO₂ and CO₃ adsorbed on Ag(110) was studied with high-resolution electron energy-loss spectroscopy (EELS). CO₂ does not adsorb on the clean surface at 100 K. EELS results show that preadsorbed atomic oxygen can induce adsorption and reaction with CO₂ to form a stable surface carbonate as well as a molecular CO₂ binding state at 100 K. The latter desorbs at 130 K while CO₃ decomposes to CO_2(g) and O_(a) at 480 K as shown by both EELS and thermal desorption. The vibrational spectrum of CO_2(a) bears remarkable similarities with CO₂ gas; both the strong asymmetric stretch at 2350 cm^? and the Fermi resonance are seen. EELS measurements performed as a function of annealing temperature indicate that the carbonate species binds with one oxygen down and the other two up with respect to the surface. Additionally, an irreversible conversion between this form and that with two oxygens down does not occur.     

Competitive collisional activation in vibrational energy transfer with cyclopropane-1t1-2,2d2. A three-channel system

Vibrational energy transfer has been studied in a reacting system by the method of competitive collisional reaction “spectroscopy.” Cyclopropane-1t₁-2,2d₂ provides a three-channel competitive system which has several advantages relative to conventional absolute rate techniques for the study of collisional transition probabilities. It is found in the range 823–1123 K that both collisional efficiency and the amount of energy transferred from the hot molecule to helium bath gas molecule decline with rise temperature. This is of great importance for high temperature shock tube and laser decomposition systems.     

Ã2Σ+g → X̃2Πu emission band system of dicyanoacetylene radical cation in the gaseous phase

The emission spectrum of the dicyanoacetylene radical cation has been observed in the 580–720 nm wavelength region as a result of low energy electron impact excitation in a crossed-beam arrangement. The band system is attributed to the òΣ⁺_g → X?²Π_u electronic transition by comparison with the photoelectron spectroscopic and calculated data on the states of dicyanoacetylene cation. The frequencies of the three Σ⁺_g vibrational fundamentals in the ground cation state have been deduced from the emission spectrum. The lifetime of the lowest vibrational level of the òΣ⁺_g state of dicyanoacetylene cation was determined to be 13 ± 2 ns. Emission could not be detected from the corresponding states, òΣ⁺, of fluorocyanoacetylene and cyanoacetylene cations, and these results are discussed.     

Vibrational relaxation of CO2(0001) in pure CO2

The rate constant for collisional deactivation of CO₂(00⁰1) in pure CO₂ has been measured at room temperature using the laser fluorescence technique. The relaxation rate has been found to be (1.0 ± 0.2) × 10^?14 cm³ s^?1 which is in favorable agreement with previously published values.     

On the use of mass scaled cluster coordinates to describe polyatomic molecule reaction dynamics: Application to O + CS2 → SO + CS

We explore the use of mass scaled cluster coordinates to describe polyatomic molecule reaction dynamics. These coordinates provide the natural extension to polyatomic systems of the familiar atom—diatom model of “rolling a marble” on a skewed and scaled potential surface in that they reduce the kinetic energy of an arbitrary system to one equivalent to that of a single mass point moving in 3N - 3 dimensions. For any given number of atoms, usually several distinct types of mass scaled cluster coordinates can be introduced, all of which are interrelated by orthogonal transformations, and many of which are convenient for describing trajectory motion in one or more arrangement channels. We illustrate these points by an application to the collinear O + CS₂ → SO + CS reaction. For this system, the reagent to product coordinate transformation is conveniently described in terms of two Euler angles α and β, for which β is analogous to the atom—diatom skew angle, and α determines how the reagent vibrational normal modes relate to the product degrees of freedom. Examination of trajectory behavior indicates that the rather small value of π - α (21.7°) leads to a rather clean correlation between CS₂ asymmetric stretch motion and product CS vibrational motion, and between CS₂ symmetric stretch and a combination of SO stretch and product translation. This explains why symmetric stretch mode excitation enhances the O + CS₂ reaction rate more efficiently than asymmetric stretch mode excitation. We also find for O + CS₂ (and many other reactions for which the unbroken bond does not significantly change its length during the reaction) that the reagent and product segments of the minimum energy path are coplanar. This means that a natural partitioning of the reaction dynamics exists in which motions parallel to this plane tend to be active in promoting the reaction whereas motions perpendicular tend to be inactive. A study of trajectory motions and product state energy partitioning for O + CS₂ confirms this.     

Use of13C/12C ratios for studying the origin of CO2 in sparkling wines

Summary ¹³C/¹²C ratios were measured in an attempt to determine the origin of the CO₂ in New Zealand commercial sparkling wines. This technique enabled a distinction to be made between CO₂ originating from C-3 plants, C-4 plants and that originating from an industrial source. With the additional measurement of the alcohol¹³C/¹²C ratios, it was possible to draw conclusions as to the wine making techniques used.

---

Anwendung von¹³C/¹²C-Isotopenverhältnismessungen zur Bestimmung der CO₂-Herkunft in Handelssekt

Zusammenfassung Die Messung von¹³C/¹²C-Isotopenverhältnissen wurde dazu benutzt, um in neuseeländischem Handelssekt den Ursprung des CO₂ zu bestimmen. Mit dieser Methode konnte zwischen CO₂ aus C-3- und aus C-4-Pflanzenprodukten und CO₂ technischen Ursprungs unterschieden werden. Bei zusätzlichen¹³C/¹²C-Verhältnismessungen an Ethanol von Sektproben war es möglich, Rückschlüsse auf die Art der Sektherstellung zu ziehen.

     

Temperature dependence of the vibration-vibration transfer rates from CO2 and N2O excited in the (0001) vibrational level to 14N2 and 15N2 molecules

V-V transfer rates from CO₂ and N₂O excited in the (00⁰1) vibrational level to ¹⁴N₂ and ¹⁵N₂ are determined from 150 to 1200 K using the laser fluorescence method, and compared with values calculated on the basis of dipole-quadrupole interactions.     

Singlet methylene kinetics: Direct measurements of removal rates of ã1A1 and b̃1B1 CH2 and CD2

Rate constants for collisional removal of ã¹A₁ and b?¹B₁ CH₂ and CD₂ have been directly measured, using IR laser induced multiple photon dissociation to prepare the radicals, and time resolved laser induced fluorescence to observe them. For CH₂(ã¹A₁) removal by He, Ne, Ar, Kr, Xe, N₂, H₂, O₂, CO and CH₄, rate constants of 3.1, 4.2, 6.0, 7.0, 16, 8.8, 130, 30, 56 and 73 × 10^?12 cm³ molecule^?1 s^?1 were found respectively. These represent significant increases over the previously accepted values. Essentially no isotope effect is observed in the removal of CD₂(ã¹A₁) by the rare gases. The rate determining step in removal by the rare gases and N₂ is thought to be singlet—triplet intersystem crossing controlled by long range attractive forces, and the results are discussed in terms of both isolated and mixed state theoretical models of these processes. For the other molecular collision partners, bimolecular chemical removal channels are possible, and may account for the relatively fast rates observed. Radiative lifetimes of five Σ vibronic levels of CH₂(b?¹B₁) and three Σ vibronic levels of CD₂(b?¹B₁) have been measured and found to lie in the range 2.5–6.0 μs, and collisional quenching rates for CH₂(b?¹B₁) are found to be of the order of the gas kinetic collisional frequency.     

Excitation and emission spectra of the 2A″2 ↽ → 2E″1 system of the gas-phase cyclopentadienyl radical

Laser-induced fluorescence excitation and resolved emission spectra of the gas-phase cyclopentadienyl radical are reported. Emission spectra following single vibronic level excitation of prominent absorption features from 338.0 to 325.6 nm are recorded and catalogued. The collision-free fluorescence lifetime is in the range of 12–20 ns. Efficient vibrational relaxation of the ²A″₂ state by SF₆ is reported. Based upon analysis of the excitation and emission spectra it is concluded that there are two or more Jahn-Teller active modes in C₅H₅. The measured spectra and our analyses agree qualitatively with recent calculations on C₅H₅ that assume three active modes with Jahn-Teller coupling parameters, λ² of 0.6–1.9.     

Vibrational excitation of SF6 in collisions with He atoms

Vibrational excitation of SF₆ molecules in collisions with He atoms is studied using a vibrational close-coupling, rotational infinite-order-sudden method of calculation. Integral and differential cross sections for excitation of the triply degenerate ν₆ and ν₅ vibrational modes of SF₆ are reported for thermal collisional energies. Excitation of the ν₆ mode is found to be particularly efficieny. The cross sections are much larger than those calculated previously for the excitation of the bending mode in the He + CO₂ system. The differential cross sections are backward peaked.     

Kinetics of O(1D) interactions with the atmospheric gases N2, N2O,H2O,H2, CO2, and O3

Rate coefficients for collisional removal of O(¹D) by six atmospheric gases have been measured by monitoring the appearance of O(³P) following photolytic production of O(¹D). The measured values, k_M±2σ, in units of 10^?11 cm^?3 molecule ^?1 s^?1 are k_O3 = 22.8±2.3, k_N2 = 2.52 ± 0.25, k_CO2 = 10.4 ± 1.0,k_H2O 195± 2.0, k_N2O = 11.7 ± 1.2, and k_H2, = 11.8±1.2.     

AB-initio Cl calculation of radiative and non-radiative decay of formaldehyde (1A2) with application to its photochemical decomposition

A method is described for an ab-initio Cl calculation of the decay of H₂CO(¹A₂). The normal modes 4, 5 and 6 turn out to be about equally important for inducing the radiative transition, while the non-radiative decay is an example of the resonance case. So the experimentally determined exponential decay must be due to a coupling with the dissociative continuum.