Chemiluminescent chemi-ionization: Ar*+Ca and the CaAr+ emission spectrum

Hartman, Dennis C.; Winn, John S.

doi:10.1063/1.441672

Cited by 11 publications

(5 citation statements)

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“…Spectroscopic studies have been carried out for all alkaline earth metal ion-argon dimers, except for the radioactive radium. [4][5][6][7][8][9][10][11][12] Dissociation energies, harmonic frequencies, anharmonic constants, and, in a few cases, equilibrium bond lengths have experimentally been determined. An analysis of these results reveals that charge-induced dipole-type interactions are sufficient to explain the trends in the data.…”

Section: Introductionmentioning

confidence: 99%

Photofragmentation spectra and structures of Sr+Arn, n=2–8 clusters: Experiment and theory

Fanourgakis

Farantos

Lüder

et al. 1998

The Journal of Chemical Physics

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The total photofragmentation cross sections of size selected Sr ϩ Ar n ,nϭ2-8, clusters have been recorded in a time of flight ͑TOF͒ mass spectrometer. In the energy range of 21 000-27 000 cm Ϫ1 three absorption bands are observed that are attributed to transitions from the ground to the three excited states that correlate to the 5p orbitals of strontium. No vibrational structure in the spectral bands is observed, even in regions where the spectrum is recorded with a resolution of 1 cm Ϫ1. The absorption spectra are calculated within a semiclassical approximation. Accurate ab initio calculations for the ground X 2 ͚ and the A 2 ͟ and B 2 ͚ excited states of Sr ϩ Ar are combined with a perturbative one-electron model, which includes the spin-orbit coupling, to construct potential energy surfaces for the excited states of all clusters. The theoretical spectra obtained without using any adjustable parameters reproduce the patterns and trends of the experimental spectra, but they are shifted to higher frequencies. A better agreement between theoretical and experimental spectra is obtained by adjusting the depth of the potential wells of the ground X 2 ͚ and excited A 2 ͟ states of the Sr ϩ Ar dimer to the experimentally estimated values. From both calculations we conclude that Sr ϩ Ar 3 is a trigonal pyramid of C 3v symmetry and Sr ϩ Ar 6 has a C 5v symmetry with five argon atoms forming a regular pentagon, one argon atom below and the cation above the pentagon plane. For these clusters, theory reproduces the characteristic blue shifts found in the absorption spectra and the splittings of the doubly degenerate states encountered in these symmetric complexes.

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Section: Introductionmentioning

confidence: 99%

Photofragmentation spectra and structures of Sr+Arn, n=2–8 clusters: Experiment and theory

Fanourgakis

Farantos

Lüder

et al. 1998

The Journal of Chemical Physics

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“…Let (PE) be the expectation value of the total Coulombic potential energy operator (which is a function of R) and let (KE) be the expectation value of the operator for the total kinetic energy of the electrons (also a function of R). The virial theorem states (KE) = -V(R) -R-jjj- (15) Therefore, given any accurate V(R), one can deduce the functions (PE) and (KE). These functions are more illuminating than V(R) alone when one wishes to discuss the changes in electronic structure that occur on binding.…”

Section: Parametersmentioning

confidence: 99%

A systematic look at weakly bound diatomics

Winn¹

1981

Acc. Chem. Res.

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This article will begin with an introductory look at various families of weakly bound diatomics and the more important representatives of each. The next section will discuss a uniform method for describing and comparing the interatomic potential energy functions of these species. Finally, the implications of these functions and comparisons among them will be discussed. This is not intended to be an all-encompassing review of weakly bound diatomics; -2-consequently, an occasional reader may find a potentially important molecule left unmentioned. I apologize for this limitation in advance, and reiterate that the goal of the article is to illuminate families of interactions and the variations in bonding exhibited among them. FAMILIES OF WEAKLY BOUND DIATOMICSA cursory glance through the Periodic Table leads one to predict most of the weakly bound homonuclear diatomics. Certainly, the rare gas dimers; He2 through Rn2, are the best known examples. In fact, the interatomic potential function for Ar 2 is as well characterized 2 as that for many common stable diatomics. The next-best known family3 is the Group II metal dimers: the alkaline earth diatomics, and Zn2, Cd2, and Hg2. The ground state atoms have closed (s2) configurations, and a formal analogy to rare gas dimers is predicted. However, as one proceeds atom by atom from the dimer to the bulk, these species revert to strongly bound metals due to the presence of low-lying sp or ds configurations. The possible role such configurations may have in the dimer bond will be discussed below.Less obvious weakly bound homonuclear diatomics can be found scattered about the Periodic Table. Atomic Mn has a 3d54s2 configuration in its ground state. The stability of the d5 configuration in this first row transition element leads to an anomalously weak binding energy 4 ' 5 for Mn 2 : De ~ 0.4 ± 0.25 eV (or6 ~ 3,500 ± 2000 cm-1). Similarly, the stability of the 4f76s2 configuration of Eu and the 4fl46s2 configuration of Yb yields anomalously weak binding, 7 and the actinide dimers Pu 2 , Am 2 and Bk 2 through No 2 are expected to be weakly bound due to the bonding ineffectiveness of the highly localized Sf electrons.8 as one moves down a Periodic Group, in contrast to the behavior of chemically bound diatomics, for which the energies generally decrease.A sufficiently large number of heteronuclear dimers have been studied to allow one to note certain trends. The majority of these dimers contain at least one rare gas, and the heteronuclear rare gas dimers are the prototypes.They provided the first arena in which simple combination rules could be tested (and found to be inaccurate).9 Three other classes that are well studied are the rare gas-monohalides, the rare gas-alkali metal dimers, and certain molecular ions. If the reader would stop for a moment and picture in his or her mind the potential energy function for a favorite strongly bound diatomic graphed on the same scale as the potential function for a weakly bound diatomic, the imagined graph would probably look like the one ...

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“…The field-free fluorescent channels of this system have been reported. 16 The new channel described here, Ar *( 3 P 2°) +Ca +hv -Ar +Ca + (5/> 2 P) +e ~, has been discussed as a likely one for the study of field-modified collisional ionization. 17 In this process, hv equals (approximately) the energy difference between Ar* and the 5/?…”

mentioning

confidence: 97%

“…This system has been well studied in the fieldfree case 16 and is, with two possible exceptions, free of any atomic absorptions by reactants or products in the wavelength region of interest, 5940-6000 A. The first exception is the twophoton process Ca(4s 21 S) -Ca(4s5s 1 S) at 6001 A which fluoresces through Ca(4s4^1P) to the ground state.…”

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Resonant Light Absorption in a Penning-Ionization Collision

1981

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The opening of a new channel of excitative Penning ionization by a collision-complex absorption of laser light has been observed in the system Ar*( 3 P) + Ca. Two relatively broad resonances at 5958 and 5990 A were found, corresponding to the production of Ca + (5£ 2 P 3 /2) and Ca + (5£ 2 Pi/2), respectively. The data indicate that the laser-assisted Penning-ionization cross section to these states exceeds that of the field-free ionization to Ca + (4£ 2 P 3/2 ).A new category of related phenomena is the spectroscopy and dynamics of radiative processes involving the transient species which exist for the duration of a bimolecular collision. 1 " 11 These processes are characterized by absorption or emission of light at wavelengths which are not resonant with the constituent elements of the transient species before or after the collision. This paper considers laser-field-modified Penning ionization (PI). Radiative collisional ionization has generated considerable theoretical interest, 12 "" 15 and the work of George and co-workers 15 has indicated that field-modified systems which undergo Penning ionization in the absence of radiation may enjoy an enhanced cross section in the presence of the laser field.We report here the first observation of a resonant, field-modified excitative channel in the system Ar*( 3 P 2°) +Ca( 1 S). The field-free fluorescent channels of this system have been reported. 16 The new channel described here, Ar *( 3 P 2°) +Ca +hv -Ar +Ca + (5/> 2 P) +e ~, has been discussed as a likely one for the study of field-modified collisional ionization. 17 In this process, hv equals (approximately) the energy difference between Ar* and the 5/? 2 P state of Ca + , as illustrated in Fig. 1.This system has been well studied in the fieldfree case 16 and is, with two possible exceptions, free of any atomic absorptions by reactants or products in the wavelength region of interest, 5940-6000 A. The first exception is the twophoton process Ca(4s 21 S) -Ca(4s5s 1 S) at 6001 A which fluoresces through Ca(4s4^1P) to the ground state. The second is the possible interference by two-photon excitation of Ar* to the n = 15-20 levels, which can ionize Ca to a level with a cascade component that we would ultimately monitor. A quantum-defect calculation 19 (accurate to ±1 cm" 1 ) was used to estimate the location of these resonances; they are not seen in the spectra reported here.The new channel can be viewed as the excitative photoionization of the (autoionizing) quasimolecule CaAr* from a continuum state to an excited (and also unbound) state of CaAr + that correlates to Ca + (5£ 2 P) + Ar( 1 S). This Ca + state has a radiative lifetime 20 of 34 nsec. It decays predominantly (80%) to the 5s level, which subsequently decays to the 4/> doublet at 3737 and 3706 A. These latter emissions determine the number of 5p 2 P ions formed (see Fig. 1).The experiments were performed using the flowing afterglow chemiluminescence apparatus described previously. 16 A dc discharge generates < _ s o o -N.

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Chemiluminescent chemi-ionization: Ar*+Ca and the CaAr+ emission spectrum

Cited by 11 publications

References 22 publications

Photofragmentation spectra and structures of Sr+Arn, n=2–8 clusters: Experiment and theory

Photofragmentation spectra and structures of Sr+Arn, n=2–8 clusters: Experiment and theory

A systematic look at weakly bound diatomics

Resonant Light Absorption in a Penning-Ionization Collision

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