Electron Impact Excitation Functions Research Articles

Change in resonance parameters of a linear molecule as it bends: Evidence in electron-impact vibrational transitions of hot COS and CO2 molecules*

Inelastic and superelastic electron-impact vibrational excitation functions of hot carbonyl sulphide COS (and hot CO2) are measured for electron energies from 0.5 to 3.0 eV (1.5 to 6.0 eV) and at a scattering angle of 90°. Based on the vibrational populations and the principle of detailed balance, these excitation functions are decomposed into contributions from state-to-state vibrational transitions involving up to the second bending overtone (030) in the electronically ground state. Both the 2 Π resonance for COS around 1.2 eV and the 2 Π u resonance for CO2 around 3.8 eV are shifted to lower energies as the initial vibrational state is excited in the bending mode. The width of the resonance hump for COS changes only little as the molecule bends, whereas that of the overall boomerang resonance for CO2 becomes narrower. The angular distribution of the electrons resonantly scattered by hot COS and hot CO2 is also measured. The different shapes depending on the vibrational transitions and gas temperatures are discussed in terms of the symmetry of the vibrational wave functions.

Excitation dynamics and post-collision interaction for lowest autoionizing states in Li and Li2 excited by electron impact

The ejected-electron spectra in the region of the lowest autoionizing states in Li and have been studied at an observation angle of 54.7° over the electron-impact energy range 0–6 eV above the excitation threshold at 56.4 eV. The strong near-threshold resonance excitation has been revealed for the and (1s → 3σg)1Σ+g molecular transitions. For the atomic , and molecular states the post-collision interaction (PCI) energy shift of corresponding lines has been measured and compared with electron-impact excitation functions for these states. The general appearance of the PCI data for the and states reveals a close agreement with the classical and semi-classical predictions, showing a minimal correlation between resonance excitation of the subshell and the PCI. Meanwhile, in the energy region of 0–1 eV the energy shift of the line reveals an abrupt decrease to nearly zero values, similar to that observed earlier for the (np5(n+1)s2)2P3/2 lines in the ejected-electron spectra of Na (n = 2) and K (n = 3) atoms. The calculations show the possibility for extrema of the PCI shift to appear in those energy regions where the negative-ion resonances are present in the excitation function of the state.

Spiro[4.4]nonatetraene and its Positive and Negative Radical Ions: Molectronic Structure Investigations

The electronic structure of spiro[4.4]nonatetraene 1 as well as that of its radical anion and cation were studied by different spectroscopies. The electron-energy-loss spectrum in the gas phase revealed the lowest triplet state at 2.98 eV and a group of three overlapping triplet states in the 4.5 – 5.0 eV range, as well as a number of valence and Rydberg singlet excited states. Electron-impact excitation functions of pure vibrational and triplet states identified various states of the negative ion, in particular the ground state with an attachment energy of 0.8 eV, an excited state corresponding to a temporary electron attachment to the 2b1 MO at an attachment energy of 2.7 eV, and a core excited state at 4.0 eV. Electronic-absorption spectroscopy in cryogenic matrices revealed several states of the positive ion, in particular a richly structured first band at 1.27 eV, and the first electronic transition of the radical anion. Vibrations of the ground state of the cation were probed by IR spectroscopy in a cryogenic matrix. The results are discussed on the basis of density-functional and CASSCF/CASPT2 quantum-chemical calculations. In their various forms, the calculations successfully rationalized the triplet and the singlet (valence and Rydberg) excitation energies of the neutral molecule, the excitation energies of the radical cation, its IR spectrum, the vibrations excited in the first electronic absorption band, and the energies of the ground and the first excited states of the anion. The difference of the anion excitation energies in the gas and condensed phases was rationalized by a calculation of the Jahn-Teller distortion of the anion ground state. Contrary to expectations based on a single-configuration model for the electronic states of 1, it is found that the gap between the first two excited states is different in the singlet and the triplet manifold. This finding can be traced to the different importance of configuration interaction in the two multiplicity manifolds.

The structure of triply excited, negative-ion resonances in the autoionizing region of helium

The formation and decay of the two lowest-lying, triply excited resonances in the autoionizing region of the helium spectrum (57-60 eV) have been studied by measuring electron-impact excitation functions for the n = 2 singly excited states of helium as a function of electron scattering angle. These results offer unambiguous confirmation of the classification of these states as and , respectively. Furthermore, the observation of the relative strengths of the decay of these features into the various final states enables some speculation as to the structure of the three excited electrons.

Fluorescence of complex molecules in crossed electron and molecular beams

Investigation of the interaction of various particles with polyatomic molecules is a complex problem having fundamental and applied significance. Complex organic molecules serve as transformers of various types of excitation into spontaneous and stimulated emission of light; a low-temperature plasma in the vapors of complex organic compounds is used, for example, in plasmachemistry. For the diagnostics of plasma and its simulation, it is necessary to know the constants of the elementary processes of energy transfer during the interaction of its constituent particles. First of all, this relates to the cross-sections for the excitation of atoms and molecules by electrons and to the dependence of these cross-sections on the energy of the electrons (the excitation function). A relatively large amount of information has been accumulated by now on atoms and simple molecules; for complex molecules the number of works is limited, and the absolute cross-section for excitation was not known at all until recently. The authors should single out the investigations of electron impact excitation functions in crossed electron and molecular beams and the works dealing with the study of inelastic scattering of electrons in crossed beams and a gas-filled cell. The method of crossed beams is the most universal onemore » for investigating the interaction of a molecule with an exciting electron, since it provides information about the behavior of an isolated molecule. The purpose of the present work was to construct a facility for studying the functions of excitation of an isolated molecule by electron impact, to measure the absolute values of the cross-section for excitation of fluorescence, and to investigate the fluorescence kinetics upon electronic excitation with nanosecond time resolution for a number of compounds.« less

Electron impact excitation of the singlet and triplet [formula omitted] states of ethylene near threshold

The electron impact excitation functions of the 1 3 B 1 u and 1 1 B 1 u π → π ∗ states of ethylene are measured. The triplet excitation function has a broad peak near 6.5 eV that is attributed to the π −1(π ∗) 2 anion state, and the singlet excitation function displays sharp structure near threshold due to the π −1(3s) 2 anion state.

Feshbach resonances in electron excitation functions of HBr

Electron impact excitation functions for b 3 Pi 1, b 3 Pi 0 and C1 Pi states of HBr have been measured in an energy range from threshold to 2.5 eV above and for scattering angles from 40 degrees to 120 degrees . Strong threshold excitation and a large number of structures in the investigated energy range are interpreted in terms of resonances, reported by Spence and Noguchi (1975) in a transmission experiment. A new resonance has been found at 10.15 eV appearing strongly at large angles in the states involving the (2 Pi 12/) core. The almost constant value of the energy separation between the members of the resonance pairs, selectivity of resonance decay with respect to the excited state ionic core and observed angular dependences have been used in discussing the resonance state assignments.

A laser-induced fluorescence study of resonance structure in the electron impact excitation functions of metastable neon and helium

The technique of laser-induced fluorescence (LIF) following electron impact excitation is used to examine the neon 3P0 and 3P2(M/sub /J) and the helium 21S metastable cross sections near threshold. In each case resonance structure is observed. The branching ratio of resonance features into the two neon metastable channels is discussed.

The observation of resonance structure in electron impact excitation functions of inner-shell states of CO

The first observation of resonance structure in electron impact excitation functions of the inner-shell (1 s)-1(2 p pi )1,3 Pi states of CO is reported. The ratio of these excitation functions shows a resonance structure at approximately 14 eV above the excitation threshold of these states. This resonance is the analogue of the 15.5 eV shape resonance in NO, the equivalent core molecule of CK*O.

Near-threshold electron impact excitation functions of high-n states of Ar, Kr, Xe, H2, N2and CO

Excitation functions of Rydberg states lying within a band of n values that is typically from approximately 16 to 46 have been measured with high energy resolution. All the excitation functions are found to have a sudden threshold onset, the sharpness of which is consistent with the high-n excitation cross sections having finite values at threshold. This behaviour, and also the details of the energy dependences of the excitation functions near to, but above the threshold, are interpreted in terms of the high-n states being formed by the evolution of the collision complex along the Wannier ridge.

High-resolution electron impact excitation functions of metastable states of neon, argon, krypton and xenon

Electron impact excitation of the lowest-lying metastable states of neon, argon, krypton and xenon have been studied as a function of incident electron energy over the range from threshold to the 2P1/2 ionisation potential and at an energy resolution of 20 meV or better. A wealth of structure is observed. Several of the features are very narrow and are coincident in energy with excited states having the classification np5n'p(J=0), while several other features correspond to pairs of resonances that have almost the same energy splitting as that of the corresponding grandparent ion doublet. The interpretation of the structures and classification of the resonances are discussed.

Electron-impact excitation of the potassium atom

Absolute optical electron-impact excitation functions for 24 transitions of the sharp, principal, diffuse, and fundamental spectral series of potassium have been measured. The determination of the density of the potassium vapor in the collision chamber was made by measuring the degree of transmission, by the vapor, of potassium resonance radiation generated externally in a fluorescence cell. From the measured optical excitation functions direct excitation functions have been determined for 14 states ($5S$, $6S$, $7S$, $8S$, $4P$, $5P$, $6P$, $7P$, $3D$, $5D$, $6D$, $5F$, $6F$, and $7F$) with the aid of known radiative-transition probabilities compiled in the literature. Theoretical calculations of these same 14 excitation functions, as well as $4D$ and $4F$, were carried out by means of the Born approximation. The $4P$, $5P$, $5S$, $3D$, and $4D$ direct excitation functions at intermediate energies (10-25 eV) were also calculated by the method of multistate close coupling, neglecting projectile-target-electron exchange. The high-energy (above 100 eV) Born-approximation cross sections agree with the experimental results for $4P$ and for all $S$ states, but are lower than experimental results, by 30-40%, for the $D$ and $F$ states. At intermediate energies the close-coupling excitation calculations agree well with the experimental excitation functions for $4P$ and $5P$, but are significantly higher than experimental values for $5S$ and $3D$. The discrepancies between the experimental and theoretical results are probably due to a combination of systematic experimental errors, errors in the available transition-probability values, and errors in the theoretical excitation functions introduced by the use of approximate excited-state wave functions (Hartree-Fock-Slater), or, in the case of intermediate or low energies, by the neglect of projectile-target-electron exchange. The polarization of the $4P\ensuremath{-}4S$ and $3D\ensuremath{-}4P$ radiation produced by electron impact was measured, and the results were used to determine the direct excitation functions of the separate magnetic sublevels of the $4P$ state.

Electron impact excitation of theHg(6P0,23)metastable states

Electron impact excitation functions for the Hg(6 /sup 3/P/sub 0//sub ,//sub 2/) metastable states were measured from threshold to 8.5 eV. The 6 /sup 3/P/sub 0//sub ,//sub 2/ states were detected by monitoring the forbidden photon emission. The 6 /sup 3/P/sub 2/ state was also selectively detected by monitoring the 2537-A emission from collisional deexcitation to the 6 /sup 3/P/sub 1/ state followed by radiative decay to 6 /sup 1/S/sub 0/. Structure observed in the excitation functions appears to be due to autoionization of short-lived excited states of Hg/sup -/. The ratio of cross sections for formation of the 6 /sup 3/P/sub 2//sub ,//sub 0/ states, sigma/sub 2//sigma/sub 0/, determined at the peak of the 6 /sup 3/P/sub 2/ excitation function (E approx. = 5.8 eV), is 9.1. The ratio of cross sections at the peak of each excitation function (6 /sup 3/P/sub 2/, E approx. = 5.8 eV; 6 /sup 3/P/sub 0/, E approx. = 5.2 eV) is 5.2. (AIP)

Resonant structure in electron impact excitation of CO near threshold

Electron impact excitation functions of numerous states in CO have been measured at 45° scattering angle with resolutions of 16–23 meV FWHM. The decay peak of the 10.04 eV resonance can be seen in the results for the a 3Π, a′ 3Σ+, and A 1Π vibrational levels. There was no evidence of resonant excitation of the a′ 3Σ+ state near 8 eV as suggested by Newton and Thomas. Excitation functions of the b 3Σ+, B 1Σ+, C 1Σ+, c 3Π, and E 1Π states, and a previously unobserbed state at 11.26 eV show numerous sharp resonances in the first few eV above threshold. Energy loss spectra in the 8–14 eV loss region show peaks corresponding to known states as well as to unidentified states. No sign of the metastable state at about 9.5 eV seen by Wells, Borst, and Zipf could be detected in direct excitation, but an indirect excitation process involving the A 1Π state is consistent with the data.

ChemInform Abstract: ELECTRON IMPACT EXCITATION OF FLUORESCENCE IN BENZENE, TOLUENE, AND ANILINE

Electron impact excitation functions for fluorescence from benzene, toluene, and aniline are measured under low pressure conditions (∼1 × 10−5 torr) with an electron energy resolution of 0.3 eV. Each excitation function exhibits a number of features, including several sharp peaks at electron energies below 20 eV. Possible identifications of these features are discussed, with the result that for each molecule at least one of the low‐energy peaks is assigned as a new resonance which decays to produce the lowest excited singlet state S1.

ChemInform Abstract: ELECTRON IMPACT EXCITATION OF METASTABLE STATES OF BENZENE, TOLUENE, AND ANILINE

Electron impact excitation functions for the formation of metastable states of benzene, toluene, and aniline are measured under low pressure conditions (∼1 × 10−5 torr) with an electron energy resolution of 0.3 eV. Considerable evidence is presented for assigning these metastables as the lowest triplet states T1. Each excitation function exhibits several features at low electron energy (4–15 eV), which are interpreted in terms of resonances which decay to give T1 and nonresonant exchange excitation processes. Comparison of these triplet excitation functions with the optical excitation functions for fluorescence (see the preceding paper) indicates that intersystem crossing does not make a major contribution to T1 formation under the present experimental conditions. From time‐of‐flight measurements a lower limit of 500 μsec is estimated for the lifetime of the lowest triplet state T1 for these three molecules.

Role of resonances in the electron-impact excitation functions of theC Πu3andE Σg+3states ofN2

Role of resonances in the electron-impact excitation functions of the<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>C</mml:mi><mml:mi> </mml:mi><mml:mrow><mml:mmultiscripts><mml:mrow><mml:mi>Π</mml:mi></mml:mrow><mml:mrow><mml:mi>u</mml:mi></mml:mrow><mml:mrow /><mml:mrow /><mml:mrow /><mml:mprescripts /><mml:mrow /><mml:mrow><mml:mn>3</mml:mn></mml:mrow><mml:mrow /><mml:mrow /></mml:mmultiscripts></mml:mrow></mml:math>and<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>E</mml:mi><mml:mi> </mml:mi><mml:mrow><mml:mmultiscripts><mml:mrow><mml:mi>Σ</mml:mi></mml:mrow><mml:mrow><mml:mi>g</mml:mi></mml:mrow><mml:mrow><mml:mo>+</mml:mo></mml:mrow><mml:mrow /><mml:mrow /><mml:mprescripts /><mml:mrow /><mml:mrow><mml:mn>3</mml:mn></mml:mrow><mml:mrow /><mml:mrow /></mml:mmultiscripts></mml:mrow></mml:math>states of<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">N</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>

Electron impact excitation of metastable states of benzene, toluene, and aniline

Electron impact excitation functions for the formation of metastable states of benzene, toluene, and aniline are measured under low pressure conditions (∼1 × 10−5 torr) with an electron energy resolution of 0.3 eV. Considerable evidence is presented for assigning these metastables as the lowest triplet states T1. Each excitation function exhibits several features at low electron energy (4–15 eV), which are interpreted in terms of resonances which decay to give T1 and nonresonant exchange excitation processes. Comparison of these triplet excitation functions with the optical excitation functions for fluorescence (see the preceding paper) indicates that intersystem crossing does not make a major contribution to T1 formation under the present experimental conditions. From time-of-flight measurements a lower limit of 500 μsec is estimated for the lifetime of the lowest triplet state T1 for these three molecules.

Electron impact excitation of fluorescence in benzene, toluene, and aniline

Electron impact excitation functions for fluorescence from benzene, toluene, and aniline are measured under low pressure conditions (∼1 × 10−5 torr) with an electron energy resolution of 0.3 eV. Each excitation function exhibits a number of features, including several sharp peaks at electron energies below 20 eV. Possible identifications of these features are discussed, with the result that for each molecule at least one of the low-energy peaks is assigned as a new resonance which decays to produce the lowest excited singlet state S1.

Excitation functions for the formation of metastable He and Ar by electron impact

The authors report the measurement of the electron impact excitation functions from threshold to 200 eV, for the formation of metastable helium and argon, using the time of flight technique. Both excitation functions have a broad maximum approximately 10 eV above threshold. Near threshold the results are in excellent agreement with earlier measurements, but they are in serious disagreement with the results of Kuprianov, the only previous measurements available over a large energy range. Recent plane and distorted wave Born approximation calculations for argon give a poor representation of the data.