States Of AlO Research Articles

Transition probabilities of the X1Σ+, A1Π, B1Δ, C1Σ+, and D1Π states of the AlO+ cation

ABSTRACTThis study computes the potential energy curves of the X1Σ+, A1Π, B1Δ, C1Σ+, and D1Π states of AlO+ cation and the transition dipole moments between them. The orders of the rotationless radiative lifetimes are 10–100 μs for the A1Π state, 1–1000 ms for the B1Δ state, 10 ns for the first well and 100 ns for the second well of the C1Σ+ state, and 1 μs for the D1Π state. Emissions of the B1Δ–A1Π and D1Π–C1Σ+ systems are so weak that they are hardly measured via spectroscopy, the emissions of the C1Σ+–X1Σ+, C1Σ+–A1Π, and D1Π–X1Σ+ systems are so strong that they can be detected readily, and emissions of the A1Π–X1Σ+ and D1Π–A1Π systems can be observed through spectroscopy only by a significant effort. There is a strong great similarity between spontaneous emissions of the A1Π–X1Σ+ system of the AlO+ cation and the A2Π–X2Σ+ system of the AlO radical. The emissions of the A2Π–X2Σ+ system of the AlO radical have been measured in outer space Therefore, it is highly possible that the emissions of the A1Π–X1Σ+ system of the AlO+ cation can be detected in the astrophysical media.

Rotational spectroscopy of AlO

The detection of rotational transitions of the AlO radical at millimeter wavelengths from an astronomical source has recently been reported. In view of this, rotational transitions in the ground X^2 Sigma^+ state of AlO have been reinvestigated. Comparisons between Fourier transform and microwave data indicate a discrepancy regarding the derived value of gamma_D in the v = 0 level of the ground state. This discrepancy is discussed in the light of comparisons between experimental data and synthesized rotational spectra in the v = 0, 1 and 2 levels of X^2 Sigma^+. A list of calculated rotational lines in v = 0, 1 and 2 of the ground state up to N' = 11 is presented which should aid astronomers in analysis and interpretation of observed AlO data and also facilitate future searches for this radical.

Ab initio study of the molecular vibrations and electronic structure of the X, B, D and F 2Σ + states of AlO

Molecular vibrations and electronic structure of the X 2Σ +, B 2Σ +, D 2Σ +, and F 2Σ + states of AlO are studied by carrying out ab initio configuration interaction calculations and molecular vibration calculations using accurate potential energy functions. An avoided crossing between the D 2Σ + and F 2Σ + potential energy curves occurs in the neighborhood of 4.0 a 0 and results in irregular vibrational levels of the D and F 2Σ + states. The vibrational constants for the F 2Σ + state are predicted from the vibrational levels not involved in the irregularity. Configuration mixing is important in describing the B, D, and F 2Σ + states. The F 2Σ + state at and around its well minimum and the D and F 2Σ + states in the avoided crossing region are characterized in terms of their main configurations and dipole moment functions.

Theoretical study of protonated aluminium oxide

Using an internally contracted multireference configuration interaction approach, threedimensional potential energy functions of the X2Σ+ (AlOH+) and X2Π (HAlO+) states have been generated. The variational calculations of the vibrational levels of AlOH+ showed that the large amplitude bending modes exhibit inverse anharmonicity and are coupled with the AlO stretching modes. The energy of the HAlO+ isomer at its equilibrium geometry and its lowest dissociation asymptote were calculated to be almost identical. A large barrier on the dissociation path prevents, however, the low lying rovibronic levels to predissociate. Using a variational Renner-Teller approach such rovibronic states for J= 1/2 and 3/2 were calculated, and strong anharmonic resonances were detected in the excited rovibronic states. The potential energy function connecting the HAlO+ and AlOH+ isomers includes a conical intersection between the 2Σ+ and the 2Π states. The barrier for isomerization relative to the AlOH+ structure was calculated to be 4·34 eV. The MRCI calculations yielded for AlO a large proton affinity of 9·35 eV. Contrary to previous theoretical studies we found that the electronic ground state of AlO+ is the 1Σ+ state and not the 3Π state. The ab initio spectroscopic constants for its three lowest electronic states are given.

Electronic quenching of the B 2Σ + state of AlO

Electronic quenching rate constants for the B 2Σ + state of AlO were determined using a pulsed-laser photolysis laser-induced fluorescence technique by examining fluorescence decay rates in the presence of seven atomic and molecular collision partners. The two polar molecules CO and NO were found to have rate constants of 4.8 × 10 −12 and 1.8 × 10 −10 cm 3 s −1, respectively. The nonpolar gases He, H 2, N 2, CO 2 and Xe were found to be poor quenchers with a bimolecular quenching rate constant having an upper bound of 1 × 10 −13 cm 3 s −1 for He, H 2, N 2 and Xe and 1 × 10 −12 cm 3 for CO 2.

Ab initio dipole moment functions for the X 2Σ+ and B 2Σ+ states of AlO

The dipole moment function for the X 2Σ+ state of AlO has been determined by a convergent sequence of MCSCF and CI calculations. It is nearly constant between R=3.0 and 4.0a0 because of a gradual transition from Al+O− to Al++O−−. This leads to a small vibrational band oscillator strength of f01=(4.0±3.0)×10−7. Several MCSCF models were tested for their ability to describe the charge transfer process, and the best model was used to study the B 2Σ+ state AlO.

Al+O3 chemiluminescence: Perturbations and vibrational population anomalies in the B 2Σ+ state of AlO

Ozone reacts with aluminum entrained in an argon buffer gas to yield the B 2Σ+–X 2Σ+ spectrum of AlO. The measured B 2Σ+ vibrational populations for this reaction follow a markedly non-Boltzmann distribution, exhibiting local maxima at vibrational levels v′=6, 8, 12, and 14. This behavior is attributed to an initial chemical reaction Al+O3→AlO(A 2Π) +O2 followed by the collision induced rearrangement AlO(A 2Π) +Ar→AlO(B 2Σ+)+Ar. The spin–orbit interaction in AlO connects ro-vibronic levels of the A 2Π and B 2Σ+ states. Consequently, collisional energy transfer is particularly efficient for the most strongly perturbed levels of the B 2Σ+ state. For Al+N2O, an approximate Boltzmann distribution in the AlO B 2Σ+ state population indicates that this reaction proceeds by a differing mechanism. Consistent with the proposed mechanism for Al+O3 is the appearance of ’’extra’’ band heads representing normally Franck–Condon forbidden A–X transitions which become allowed because of a small admixture of B 2Σ+ character. The relative intensities of the extra and ’’main’’ transitions are strongly dependent upon the argon buffer gas pressure. A quantitative description of this dependence gives an estimate for the amount of mixing between A 2Π and B 2Σ+ and for the rate of energy transfer between these two states. The measured rate constant for the most strongly perturbed level is comparable in magnitude to the rate constant expected for hard sphere collisions between argon and AlO. The present results allow some understanding of the continuum emission observed in the upper atmosphere release of aluminized grenades. They also may be pertinent to the construction of a visible chemical laser.

A suggested mechanism for the visible chemiluminescence observed in gas phase aluminum oxidation

A reaction mechanism that generates the excited ( A 2 Π) and/or lowest-lying 4 Σ + and 4 Π states of AlO is suggested as the source of the visible chemiluminescence often observed in the gas phase oxidation of aluminum. Data from upper atmospheric chemical release experiments utilizing aluminized grenades, aluminized burners, and trimethylaluminum appear to be inconsistent with previously proposed mechanisms, but can be reasonably accounted for by AlO ∗ pumping reactions of molecules containing loosely bound aluminum atoms with atomic oxygen. The prototype reaction Al 2 + O and Al + O 3 are discussed in some detail, in terms of the correlation of reactant and product states. According to the “electron-jump” model, the formation of excited AlO ∗ with high quantum efficiency can be expected as a consequence of the open shell structure of the aluminum oxide molecule.

Spin doubling in the observed2Σ+states of AlO

From high-resolution spectra obtained from low-temperature discharges, the spin doubling in several vibrational levels of the x2 Sigma +, B2 Sigma + and D2 Sigma + observed states of AlO have been calculated. The results differ completely, even in sign for B2 Sigma +, from previous determinations. A theoretical attempt is made to calculate the gamma constant for the ground state and the result appears to confirm the authors' experimental value.