The A2Σ+ ← X2Π Transition of CF Starting from Highly Excited Vibrational States

Courrèges-Lacoste, G. Bazalgette; Sprengers, J. P.; Ubachs, Wim; Stolte, S.; Linnartz, H.

doi:10.1006/jmsp.2000.8261

Cited by 13 publications

(6 citation statements)

References 14 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…This suggests the molecules are either 'trapped' in the rotational states that these transitions originate from or that they are replenished via cooling from higher states. This observation is also consistent with conclusions derived from a plasma expansion study of the A 2 Σ + -X 2 Π electronic transition of the heavier CF [35]; also here higher vibrational levels were found to be substantially populated, but rotational temperatures were low as CF can cool much easier, rotationally, given its much smaller rotational constant.…”

Section: Lower Panel)supporting

confidence: 91%

Cavity ring-down UV spectroscopy of the C2Σ+-X2Π electronic transition of CH

Linnartz

Ubachs

2019

Journal of Molecular Spectroscopy

View full text Add to dashboard Cite

Rotationally resolved spectra of the C 2 Σ + -X 2 Π electronic system of the CH radical were measured using cavity ring-down spectroscopy in supersonically expanding, planar hydrocarbon plasma. The experimental conditions allowed the study of highly excited rotational levels starting from vibrationally excited states. Here we present some 200+ new or more accurately recorded transitions in the 0-0, 1-1 and 2-2 vibronic bands in the ultraviolet between 30900-32400 cm -1 (324-309 nm). The resulting data, compared to earlier measurements, allows for the determination of more precise molecular constants for each vibrational state and therefore more precise equilibrium values. From this an equilibrium bond length of 1.115798(17) Å for the C 2 Σ + state is determined. A comprehensive list with observed transitions for each band has been compiled from all available experimental studies and constraints are placed on the predissociation lifetimes.

show abstract

Section: Lower Panel)supporting

confidence: 91%

Cavity ring-down UV spectroscopy of the C2Σ+-X2Π electronic transition of CH

Linnartz

Ubachs

2019

Journal of Molecular Spectroscopy

View full text Add to dashboard Cite

show abstract

“…Assignment of these hot bands to the four low frequency bending modes 4 0 1 6 1 1 , 4 0 1 7 1 1 , 4 0 1 8 1 1 , and 4 0 1 9 1 1 is straightforward, both based on the previous work by Guelachvili et al as well as the recent study by Zhao et al A sample portion of the slit jet cooled diacetylene infrared absorption spectra near the fundamental v 4 band origin is displayed in Figure , which highlights a small portion of rotational progressions observed in 4 0 1 7 1 1 , 4 0 1 8 1 1 bending hot bands. It is important to emphasize that these high steady state populations of excited bending states are formed and remain inefficiently cooled in a slit 1D expansion, which has a 1/ r versus 1/ r 2 density drop off and therefore ≈ 2 orders of magnitude higher collisions than experienced in a traditional 2D pinhole nozzle expansion environment. − …”

Section: Results and Analysismentioning

confidence: 99%

“…Such a high degree of bending vibrational excitation is quite unexpected for a slit jet expansion, where the density drop off is much slower (∝ 1/r) than that of a pinhole expansion (∝ 1/r 2 ) and thus providing many orders of magnitude larger number of cooling collisions. 53,56 Indeed, slit cooling of vibrational populations for stable molecules with similar bending frequencies have routinely indicated nearly equilibrium behavior in slit jet expansions between rotational and vibrational degrees of freedom. Specifically, study of the bending vibration in jet-cooled CO 2 , as well as an extensive progression of bending states in HF−CO 2 complexes, revealed essentially complete equilibrium between rotational, vibrational and even Doppler broadened translational temperatures as a function of distance downstream of the slit jet expansion orifice.…”

Section: Results and Analysismentioning

confidence: 99%

Spectroscopy and Dynamics of Jet-Cooled Polyynes in a Slit Supersonic Discharge: Sub-Doppler Infrared Studies of Diacetylene HCCCCH

Chang

Nesbitt

2015

J. Phys. Chem. A

View full text Add to dashboard Cite

Fundamental, bending (ν 6 , ν 7 , ν 8 , ν 9 ), and CC-stretch (ν 2 , ν 3 ) hot band spectra in the antisymmetric CH stretch (ν 4 ) region near 3330 cm −1 have been observed and analyzed for jet cooled diacetylene (HCC− CCH) under sub-Doppler conditions. Diacetylene is generated in situ in the throat of a pulsed supersonic slit expansion by discharge dissociation of acetylene to form ethynyl (CCH) + H, followed by radical attack (HC CH + CC−H) to form HCC−CCH + H. The combination of (i) sub-Doppler line widths and (ii) absence of spectral congestion permits rotational structure and Coriolis interactions in the ν 4 CH stretch fundamental to be observed and analyzed with improved precision. Of particular dynamical interest, the spectra reveal diacteylene formation in highly excited internal vibrational states. Specifically, multiple Π ← Π and Δ ← Δ hot bands built on the ν 4 CH stretch fundamental are observed, due to doubly degenerate bending vibrations [cis CC−H bend (ν 6 ), trans C− CC bend (ν 7 ), trans CC−H bend (ν 8 ) and cis C−CC bend (ν 9 )], as well as a heretofore unobserved Σ ← Σ band assigned to excitation of ν 2 or 2ν 3 CC stretch. Boltzmann analysis yields populations consistent with universally cold rotations (T rot ≈ 15 ± 5 K) and yet superthermal vibrations (T vib ≈ 85−430 K), the latter of which is quite anomalous for the high collision densities in a slit jet expansion. In order to elucidate the physical mechanism for this excess vibrational excitation, high level ab initio CCSD(T) calculations have been pursued with explicitly correlated basis sets (VnZ-f12; n = 2,3) and extrapolated to the complete basis set (CBS) limit using MOLPRO quantum chemistry software. The results suggest that the extensive hot band structure observed arises from (i) highly exothermic CCH + HCCH addition to yield a strongly bent HCCHCCH radical intermediate (ΔH = −62.6 kcal/mol), followed by (ii) rapid fragmentation over a submerged transition state barrier (ΔH = −18.9 kcal/mol) to form vibrationally hot diacetylene + H products (ΔH = −25.6 kcal/mol), and consistent with crossed molecular beam studies by Kaiser et al. [Phys. Chem. Chem. Phys. 2002, 4, 2950 Finally, RRKM fragmentation rates for this complex are calculated, which exceed collision frequencies in the slit jet expansion and suggest near unity quantum efficiency for diacetylene formation.

show abstract

“…It should be noted that diatomic EH and E–X (E = Si, Ge, Sn, Pb; X = F, Cl, Br, I) species, in which the doublet state is the ground electronic state, have been theoretically studied previously . Some of the E–X species, e.g., SiF, SiCl, SiBr, CF, CCl, and CBr, have also been experimentally investigated. − And there are calculations on CLi, CNa, SiLi and SiNa that confirm their quartet ground states. ,,,, …”

Section: Electronegativity As a Factormentioning

confidence: 99%

“…Though their heats of formation are all very positive, these molecules have reasonable bond energies (shown by the adiabatic energy curves in Figure S2(a) and (d) in the SI for SiLi and SiF, for example), and should be spectroscopically observable in cryogenic matrix isolation, interstellar environment (like CH), or molecular beams. As mentioned above, some of the E–X species, including SiF, SiCl, SiBr, CF, CCl, and CBr, have been observed as transient species. − The E-AM diatomics, some of our best candidates for quartet ground states, appear to be less studied, though there are calculations for some of them. ,,,, …”

Section: Dimerizationmentioning

confidence: 99%

Tuning Spin-States of Carbynes and Silylynes: A Long Jump with One Leg

Zeng

Wang

et al. 2014

J. Am. Chem. Soc.

View full text Add to dashboard Cite

The challenge motivating this paper is to induce, by chemical substitution, a silylyne, SiR, or a congeneric carbyne, CR, to adopt the high-spin quartet rather than the low-spin doublet as its ground state. The difficulty is seen in the preference for the doublet of the parent SiH (doublet-quartet energy difference ∼39 kcal/mol, favoring the doublet) or CH (∼17 kcal/mol). Strategies for having high-spin ground state parallel those for silylenes and carbenes: greater electropositivity (σ-donation) and π-acceptance of the single substituent favor the high-spin state. The electronegativity trend can be understood from an ions in molecules way of thinking already present in the literature in the works of Boldyrev and Simons, and of Mavridis and Harrison; i.e., the quartet ground state spin of some CR/SiR species is largely determined by the ground state spin of C(-)/Si(-). In this study, we provide a diabatization analysis that solidly confirms the ions in molecules picture and explains the difference in the equilibrium internuclear distances for the two spin states. In general, electronegativity dominates the ordering of spin states. π-Acceptors also help to lower the quartet state energy of the many carbynes (silylynes) examined, whose range of doublet-quartet differences calculated is impressive, 120 (100) kcal/mol. The qualitative understanding gained leads to the prediction of some quartet-ground state carbynes (CMgH, CAlH2, CZnH, CSiH3, CSiF3, etc.) and a smaller number of silylynes (SiMgH, SiMgF, SiBeH, etc.). A beginning is made on the energetics of approach geometries of the fragments in the highly exoergic dimerization of CH to acetylene; it should proceed for the ground state doublet CH through C2h-like trajectories, with no activation energy.

show abstract

The A2Σ+ ← X2Π Transition of CF Starting from Highly Excited Vibrational States

Cited by 13 publications

References 14 publications

Cavity ring-down UV spectroscopy of the C2Σ+-X2Π electronic transition of CH

Cavity ring-down UV spectroscopy of the C2Σ+-X2Π electronic transition of CH

Spectroscopy and Dynamics of Jet-Cooled Polyynes in a Slit Supersonic Discharge: Sub-Doppler Infrared Studies of Diacetylene HCCCCH

Tuning Spin-States of Carbynes and Silylynes: A Long Jump with One Leg

Contact Info

Product

Resources

About