Unexpected coexistence of radiation and absorption in rotationally excited nitrogen molecular ions

Partial EI-mass spectra of 3β-hydroxy- and 3β-acetoxy-5α-cholestanes substituted in positions 5α-, 6β- or 5α,6β- with a hydroxyl group or halogen atoms (fluorine, chlorine, bromine) are presented. The molecular ions of 5α,6β-disubstituted derivatives of 3β-hydroxy-5α-cholestane (or of its 3-acetate) are considerably more stable than the corresponding monosubstituted derivatives if at least one of the pair of the vicinal substituents is chlorine or fluorine. This increase in stability, most striking in 5α- and 6β-fluoro compounds, is explained by the inductive effect.

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Mass spectra of 4,4-dimethyl-A-homo-4a,6-cholestadien-3-ols, 4,4-dimethyl-A-homo-5-cholestene-3,4a-diols and their derivatives

Collection of Czechoslovak Chemical Communications ◽

10.1135/cccc19822768 ◽

1982 ◽

Vol 47 (10) ◽

pp. 2768-2778

Author(s):

Antonín Trka ◽

Helena Velgová

Keyword(s):

Carbon Atom ◽

Electron Impact ◽

Mass Spectra ◽

Molecular Ions

Partial electron impact induced mass spectra are given of 3α-hydroxy-, 3β-hydroxy-, 3β-methoxy-, 3α-acetoxy- and 3β-acetoxy-4,4-dimethyl-A-homo-4a,6-cholestadienes, 3α,5α-epoxy-4,4-dimethyl-A-homo-5-cholestane, isomeric 4,4-dimethyl-A-homo-5-cholestene-3α(β),4aα(β)-diols, their 3-acetoxy derivatives and 3-methyl ethers. The fragmentation of the molecular ions of these substances involves the usual elimination of substituents (in the form of H2O, CH3OH, CH3COOH, CH2CO), but the most abundant and characteristic ions are products of the contraction of ring A (to a six- or five-membered one), accompanied by expulsion of a fragment containing the carbon atom C(4) with both methyls.

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Rotational de-excitations of C3H+ (1Σ+) by collision with He: new ab initio potential energy surface and scattering calculations

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa1086 ◽

2020 ◽

Vol 494 (4) ◽

pp. 5675-5681 ◽

Cited By ~ 1

Author(s):

Sanchit Chhabra ◽

T J Dhilip Kumar

Keyword(s):

Potential Energy ◽

Potential Energy Surface ◽

Ab Initio ◽

Cross Sections ◽

Energy Surface ◽

Molecular Ions ◽

Basis Set ◽

Rate Coefficients ◽

Close Coupling ◽

Collisional Rate Coefficients

ABSTRACT Molecular ions play an important role in the astrochemistry of interstellar and circumstellar media. C3H+ has been identified in the interstellar medium recently. A new potential energy surface of the C3H+–He van der Waals complex is computed using the ab initio explicitly correlated coupled cluster with the single, double and perturbative triple excitation [CCSD(T)-F12] method and the augmented correlation consistent polarized valence triple zeta (aug-cc-pVTZ) basis set. The potential presents a well of 174.6 cm−1 in linear geometry towards the H end. Calculations of pure rotational excitation cross-sections of C3H+ by He are carried out using the exact quantum mechanical close-coupling approach. Cross-sections for transitions among the rotational levels of C3H+ are computed for energies up to 600 cm−1. The cross-sections are used to obtain the collisional rate coefficients for temperatures T ≤ 100 K. Along with laboratory experiments, the results obtained in this work may be very useful for astrophysical applications to understand hydrocarbon chemistry.

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