Ground Electronic State Of CO Research Articles

Semi-empirical ground-state potential of carbon monoxide with physical behavior in the limits of small and large inter-atomic separations

Recently, several empirical models of the potential energy function (PEF) of the ground electronic state of CO have been developed by Coxon and Hajigeorgiou using the direct-potential-fit (DPF) analysis. These models reproduce more than twenty thousand of observed ro-vibrational line positions within their experimental accuracies and follow the theoretically predicted long-range asymptotic behavior of the potential beyond Le Roy's radius. However, the applicability of these models to calculations of the intensities of weak transitions is not obvious due to limitations discussed in this work. Here, we make the next step by imposing an additional requirement that the model has to display physical behavior outside the region to which the available spectroscopic data pertain. We perform ab initio calculations of the potential in the short-range region r = 0.3–0.8 Å where the potential increases well above the dissociation limit and include these data along with the estimated uncertainties in the DPF analysis. At smaller r, our PEF tends to the well-known united-atom limit. In the long-range region, it follows the ab initio data with their estimated accuracies available in the literature. On top of the above, the model is analytical, i.e. it has continuous derivatives of all orders. The model constructed is a linear function of twenty three adjustable parameters, and a non-linear function of additional five parameters. The properties of the new PEF are investigated in comparison with the previous empirical model due to Coxon and Hajigeorgiou (2004). Our PEF provides reproduction of all observed lines at the same level of accuracy. The new potential changes the intensities of high overtone transitions dramatically. In addition, we find that the anomalies in the purely rotational and ro-vibrational spectra change their intensities between the two PEFs even for the low-v bands.

High sensitivity of the anomalies in the rotational and ro-vibrational bands of carbon monoxide to small changes in the molecular potential and dipole moment

We compare the intensities of purely rotational and ro-vibrational transitions within the ground electronic state of CO calculated with two dipole moment functions (DMFs) of Li et al. (2015) and four potential energy functions (PEFs), a semi-empirical PEF of Meshkov et al. (doi: https://doi.org//10.5281/zenodo.1198744) and three empirical ones due to Coxon and Hajigeorgiou (2004, 2016, 2017). All these PEFs reproduce the experimental line positions with similar normalized standard deviations (NSDs), and the energy mismatch between the vibrational levels with v⩽5 does not exceed 0.0002 cm−1 among all PEFs. Despite these similarities, we find that the rotational anomalies in the 0-0, 1-1, 2-2, 3-3, 4-4, and 5-0 bands shown in Figs. 3 and 4 of Medvedev et al. (2017) change their intensities by a factor of 2 to 250 among the above PEFs at a given DMF. Both the positions and intensities of the anomalies change between two DMFs at a given PEF.

Dissociation Energy and Electronic and Vibrational Spectroscopy of Co+(H2O) and Its Isotopomers

The electronic spectra of Co(+)(H(2)O), Co(+)(HOD), and Co(+)(D(2)O) have been measured from 13,500 to 18,400 cm(-1) using photodissociation spectroscopy. Transitions to four excited electronic states with vibrational and partially resolved rotational structure are observed. Each electronic transition has an extended progression in the metal-ligand stretch, v(3), and the absolute vibrational quantum numbering is assigned by comparing isotopic shifts between Co(+)(H(2)(16)O) and Co(+)(H(2)(18)O). For the low-lying excited electronic states, the first observed transition is to v(3)' = 1. This allows the Co(+)-(H(2)O) binding energy to be determined as D(0)(0 K)(Co(+)-H(2)O) = 13730 ± 90 cm(-1) (164.2 ± 1.1 kJ/mol). The photodissociation spectrum shows a well-resolved K(a) band structure due to rotation about the Co-O axis. This permits determination of the spin rotation constants ε(aa)" = -6 cm(-1) and ε(aa)' = 4 cm(-1). However, the K(a) rotational structure depends on v(3)'. These perturbations in the spectrum make the rotational constants unreliable. From the nuclear spin statistics of the rotational structure, the ground state is assigned as (3)B(1). The electronic transitions observed are from the Co(+)(H(2)O) ground state, which correlates to the cobalt ion's (3)F, 3d(8) ground state, to excited states which correlate to the (3)F, 3d(7)4s and (3)P, 3d(8) excited states of Co(+). These excited states of Co(+) interact less strongly with water than the ground state. As a result, the excited states are less tightly bound and have longer metal-ligand bonds. Calculations at the CCSD(T)/aug-cc-pVTZ level also predict that binding to Co(+) increases the H-O-H angle in water from 104.1° to 106.8°, as the metal removes electron density from the oxygen lone pairs. The O-H stretching frequencies of the ground electronic state of Co(+)(H(2)O) and Co(+)(HOD) have been measured by combining IR excitation with visible photodissociation in a double resonance experiment. In Co(+)(H(2)O) the O-H symmetric stretch is ν(1)" = 3609.7 ± 1 cm(-1). The antisymmetric stretch is ν(5)" = 3679.5 ± 2 cm(-1). These values are 47 and 76 cm(-1), respectively, lower than those in bare H(2)O. In Co(+)(HOD) the O-H stretch is observed at 3650 cm(-1), a red shift of 57 cm(-1) relative to bare HOD.

The Potential Energy Function for the X1Σ + Ground State of CO

By means of a purely quantum mechanical method, we construct an accurate potential energy function for the X 1Σ + ground electronic state of CO from a large set of experimental frequency data for vibration-rotational bands of several isotopic species. We use an analytical expression for the potential in the form of a Dunham series for the Born-Oppenheimer part plus mass-dependent corrections. A total of 19 parameters are necessary in order to represent the potential energy function capable of reproducing with good accuracy the set of more than 10 000 high-quality transition frequencies.

Vibration-rotational matrix elements for infrared transitions of diatomic molecules

Theoretical expressions for the vibro-rotational matrix elements corresponding to i.r. transitions vJ→ v′ J′ with v ⩽ v ′ ⩽ v + 6 are obtained in terms of quadratic polynomials in m, including contributions from the Dunham potential energy parameters a 1 to a 5 and from dipole-moment expansion coefficients M 0 to M 7. The formalism has been applied to vibrational transitions in the ground electronic state of CO and HCl. The Herman-Wallis coefficients have been derived for the bands 0-0 to 0-4 of CO and 0-0 to 0-6 of HCl and are compared with experimental data.

On the vibration-rotational matrix elements for diatomic molecules

Theoretical expressions for the vibro-rotational matrix elements of powers of the reduced displacement from equilibrium, corresponding to the infrared and Raman transitions vJ→ v′J′ with v′⩽ v+4, are obtained in terms of quartic polynomials in m (or J), including contributions from theDunham potential-energy coefficients a 1, a 2, a 3. It is shown that it is preferable to consider the coefficients of the vibration-rotation interaction function [F v′ v(m)] 1 2 rather than the Herman-Wallis factors. Two formalisms derived from power series expansion of the vibration-rotational internuclear potential function have been applied to the infrared transitions v→ v′ (with v = 0, 10, 20) of the ground electronic state of CO.

Single collision ion–molecule reactions at thermal energy: Rotational and vibrational distributions from N++CO→N+CO+

A new apparatus is developed and used to obtain nascent vibrational and rotational distributions in the ground electronic state of CO+ formed from the charge transfer reaction N+(3P)+CO (X 1Σ+)→N(4S)+CO+ (X 2Σ+,v,J)+0.52 eV, at approximately thermal energies. The device utilizes a flow tube for the production of thermal N+ ions in a helium buffer and a large diameter sampling orifice which delivers the ions via a mild free jet expansion into a low pressure chamber. The expansion is crossed by a stream of reactant CO molecules and the CO+ product states are probed by laser-induced fluorescence. Although the energy available is sufficient to populate CO+ vibrational states up to v″=2, the major vibrational channel in the CO+ product is v″=0. The relative vibrational distribution is found to be: Nv=0≳0.81 (observed under single collision conditions), Nv=1<0.15 (not observed), and Nv=2≊0.04 (observed only under nonsingle collision conditions). The rotational distribution in the v″=0 state is characterized closely by a Boltzmann distribution with a temperature of 410±50 K. This represents a fractional energy disposal into rotation of only 2%. Nearly all of the reaction exothermicity is therefore released into translational recoil. These results are considered in terms of simple dynamical models of the charge transfer process.

Ejected-electron spectroscopy of autoionising states of CO using an electron-electron coincidence technique

Quantitative measurements have been made of the relative intensities for electron-emitting transitions from autoionising levels of carbon monoxide to vibrational levels of the ground electronic state of CO+, following electron impact excitation. An electron-electron coincidence technique was used, in which the scattered electrons which had excited a selected autoionising level, and ejected electrons resulting from subsequent autoionisation processes were detected in separate analysers. The measured intensities are compared with Franck-Condon calculations using Morse potentials to represent the autoionising levels and ion levels. The results obtained indicate that the equilibrium internuclear separation for the autoionising levels is 1.243+or-0.001 AA, very close to that for the A2 Pi state of CO+, which is the probable series limit. Previous assignments of the autoionising levels, based on photoabsorption and photoelectron spectra, are discussed in the light of the present results.

The fundamental bands of CO as chromospheric indicators in late-type giant stars

Synthetic spectra are presented for the vibrational-rotational fundamental transitions (XV=1) in the ground electronic state of CO for the upper-photosphere--lower-chromosphere atmospheric model of Arcturus derived by Aryes. It is found that the CO spectrum is formed in LTE and the strongest molecular lines exhibit emission cores reflecting the chromospheric temperature rise. The CO fundamental bands offer an excellent observational probe for the presence of stellar chromospheres and a consistency check for chromospheric models derived from traditional chromospheric indicators. (AIP)

Ground electronic state and geometry of the CO ? 3 radical anion

The ground electronic state of CO–3 has been shown by ab initio calculations to be a 2B1 state. It has a structure of C2v symmetry with a unique OCO angle of 131.36°. Calculated results show that EHT and INDO methods have failed to predict the structure of this species.

Pulsed stimulated emission due to vibrational transitions in the carbon monoxide molecule

An investigation was made of pulsed stimulated emission due to vibrational transitions in the ground electronic state of CO excited by discharges in pure CO and in mixtures of CO with helium, argon, and xenon. It was found that the output power, shape and duration of the output pulses, and spectral composition of the stimulated radiation were different when discharges took place in pure CO from the corresponding parameters obtained for mixtures. Moreover, the discharge conditions had a strong influence on all these parameters. The experimental results indicated that different mechanisms of the population inversion of the active levels took place in the investigated mixtures. Allowance for the excitation and deexcitation of the vibrational levels by electrons, collisional exchange of the vibrational quanta (ν-ν exchange), and excitation via higher electronic states of the molecules explained the experimental observations.

Threshold energy electron impact excitation of carbon dioxide and carbon disulphide

The threshold energy electron impact excitation spectra of CO 2 and CS 2 have been studied using the sulfur hexafluoride scavenger technique. The main results are triplet state excitation and autoionisation of negative ions associated with resonant excited states of the molecules. This confirms previous data concerning diatomic molecules. Furthermore, transitions such as 1Π g−X 1Σ g + and 1Π u−X 1Σ g + are only weakly induced by low energy electrons, while the corresponding triplet excitations are probably more easily produced. Structures at 5.6, 6.1 and 6.6 eV observed in CS 2 are due to negative ions and/or to 3Π u, 3Π g excitation. The autoionisation of CO 2 −(X 2Π u) proceeds also by ejection of a thermal energy electron and leads to highly excited vibrational levels (3–5 eV) of the ground electronic state of CO 2.

Electron Impact near theaΠ3State of CO: Dipole-Dominated Resonances

Sharp structures have been observed in the elastic and vibrational ($v=1$ and $v=2$) cross sections of the ground electronic state of CO at energies coincident with the $v=0, 1, \mathrm{and} 2$ levels of the $a^{3}\ensuremath{\Pi}$ state of CO. The large electric dipole moment of the $a^{3}\ensuremath{\Pi}$ state of CO (1.38 D) appears to be sufficient to bind temporarily the incoming electron at or near the top of the potential well. The potential energy curve for this "dipole-dominated resonance" coincides with that of the $a^{3}\ensuremath{\Pi}$ state.

Electronic Transition Moment Integrals for First Ionization of CO and the A - X Transition in CO+. Some Limitations on the use of the r-Centroid Approximation.

Integrals necessary for the determination of transition moment matrix elements from experimental data have been evaluated numerically by use of vibrational wave functions derived from RKR potentials. A power series expansion for the electronic transition moment has been assumed. The significant quantities which can be related to an arbitrary center of expansion are vibrational overlap integrals and quantities of the form ʃψ v' r n ψ v″ dr. Experimental band intensities and relative populations for vibrational levels of the initial electronic state are needed to determine the expansion coefficients. Transition moment integrals have been calculated for first ionization from the ground electronic state of CO and for the A 2Π i - X 2Σ+ transition of CO+. Comparison of these integrals with previous calculations based on Morse functions has shown them to be rather sensitive to the wave-functions [potentials] used. Characteristics generally attributed to the r-centroid and related integrals are examined, and some limitations on the use of the r-centroid approximation are discussed, following a review of assumptions made in the use of that approximation.