Atoms

9 pages, 2276 KiB

Open AccessArticle

Detection of Optogalvanic Spectra Using Driven Quasi-Periodic Oscillator Dynamics

by Mark Koepke

Atoms 2024, 12(8), 42; https://doi.org/10.3390/atoms12080042 - 19 Aug 2024

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The narrowband light from a scannable, single-mode dye laser influences the electrical properties of gas discharges. The variation in these properties as the laser wavelength λ is scanned yields the optogalvanic spectrum of the discharge (i.e., electrical conductivity vs. frequency). By connecting a neon lamp, capacitor, and power supply in parallel, an undriven relaxation oscillator is formed whose natural frequency f₀ is affected by neon-resonant laser light and this λ-dependence of the relaxation oscillator frequency f₀ yields a variant optogalvanic spectrum (i.e., f₀ vs. frequency). In this paper, a driving force is effectively applied to an otherwise undriven oscillator when the incident light is chopped periodically at f_d. For f_d ≈ f₀ and a sufficiently large driving force amplitude (laser intensity and the degree of neon resonance), the relaxation oscillator can be entrained so that f₀ is locked on f_d and is independent of λ. For the new chopped-light technique described here, f_d is adjusted to be the subthreshold of the entrainment range, where the λ-dependence of f₀ is advantageously exaggerated by periodic pulling, and the beat frequency |f_d − f₀| vs. λ provides an optogalvanic spectrum with appealingly amplified signal-to-noise qualities. Beat frequency neon spectra are reported for the cases f_d < f₀ and f_d > f₀ and are compared with spectra obtained using the unchopped-light (i.e., undriven) method. Full article

(This article belongs to the Special Issue Plasma Physics Highlights: Non-equilibrium Dynamics, Interfaces and Mixing)

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5 pages, 2337 KiB

Open AccessObituary

Claudio Mendoza (1951–2024)

by Manuel Bautista Plaza

Atoms 2024, 12(8), 41; https://doi.org/10.3390/atoms12080041 - 9 Aug 2024

Viewed by 965

Abstract

I met Claudio in 1989 when I was starting the last year of my physics bachelor’s degree [...] Full article

(This article belongs to the Section Atomic, Molecular and Nuclear Spectroscopy and Collisions)

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11 pages, 351 KiB

Open AccessArticle

Calculation of Low-Lying Electronic Excitations of Magnesium Monofluoride: How Well Do Coupled-Cluster Methods Work?

by Marko Horbatsch

Atoms 2024, 12(8), 40; https://doi.org/10.3390/atoms12080040 - 8 Aug 2024

Cited by 1 | Viewed by 809

Abstract

Magnesium monofluoride is a polar molecule amenable to laser cooling which has caused renewed interest in its spectroscopy. In this work, we consider the case of three low-lying electronic excitations, namely

X^{2} Σ^{+}

→

A^{2} Π

, [...] Read more.

X^{2} Σ^{+}

→

A^{2} Π

X^{2} Σ^{+}

→

B^{2} Σ^{+}

X^{2} Σ^{+}

→

C^{2} Σ^{+}

, using well-developed quantum chemistry approaches, i.e., without reference to the spin-orbit splitting of the

A^{2} Π

states. Accurate experimental data for these transitions have been available for over 50 years. Here, we explore the linear response method at the level of CC2 theory, as well as equation of motion methods at the level of CCSD and CC3, using two families of basis sets. Excellent agreement is obtained for the first three transitions when using the correlation-consistent basis sets and extrapolation to the complete basis limit within EOM-CC3 (at a relative precision of

10^{- 4}

), and qualitative agreement for the other two methods. The purpose of this paper is to serve as a guide on how to approach the accurate calculation of excitations in polar diatomic molecules. Full article

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11 pages, 2412 KiB

Open AccessArticle

A Collisional-Radiative Model for Kr III Ions

by Shikha Rathi and Lalita Sharma

Atoms 2024, 12(8), 39; https://doi.org/10.3390/atoms12080039 - 29 Jul 2024

Viewed by 898

Abstract

A collisional radiative model for Kr III in the ultraviolet regime is developed. For this purpose, atomic parameters for

4 s^{2} 4 p^{4}

4 s 4 p^{5}

4 s^{2} 4 p^{3} n l

, and [...] Read more.

A collisional radiative model for Kr III in the ultraviolet regime is developed. For this purpose, atomic parameters for

4 s^{2} 4 p^{4}

4 s 4 p^{5}

4 s^{2} 4 p^{3} n l

, and

4 s^{2} 4 p^{3} 5 d

configurations with n ranging from 5 to 7 and

l = s, p

, using the multiconfiguration Dirac–Hatree–Fock method are calculated. The effects of Breit and radiative quantum electrodynamic corrections are also included. Electron impact excitation cross-sections from the ground state, along with four metastable states arising from the

4 s^{2} 4 p^{4}

configuration to all fine structure levels of interest, are calculated using the relativistic distorted wave method. The reliability of the model is tested by comparing the predicted results with the previous measurements. Full article

(This article belongs to the Section Atomic, Molecular and Nuclear Spectroscopy and Collisions)

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15 pages, 734 KiB

Open AccessReview

Electron and Positron Impact Ionization of Molecules

by Ladislau Nagy, István Tóth and Radu I. Campeanu

Atoms 2024, 12(8), 38; https://doi.org/10.3390/atoms12080038 - 23 Jul 2024

Cited by 1 | Viewed by 833

Abstract

We review our group’s most significant results concerning the collision of positrons and electrons with small molecules. Total and triple differential cross sections for the ionization of these targets were calculated in the distorted wave Born approximation using Gaussian molecular orbitals. Different models [...] Read more.

(This article belongs to the Section Atomic, Molecular and Nuclear Spectroscopy and Collisions)

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Atoms, Volume 12, Issue 8 (August 2024) – 5 articles

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