High-resolution study of the infrared band ν8 of CH3CN

Koivusaari, M.; Horneman, V.‐M.; Anttila, R.

doi:10.1016/0022-2852(92)90076-z

Cited by 28 publications

(31 citation statements)

References 15 publications

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“…The possibility that the vibrationally excited levels of CH 3 CN are radiatively pumped by 27 µm radiation was originally suggested by Goldsmith et al (1983). Using the laboratory measurement of the spontaneous decay rate of the v 8 = 1 band of CH 3 CN, A vib ≈ 1.6 × 10 −2 s −1 (Koivusaari et al 1992), and adopting for the collision cross section the same value as for the vibrational ground state, < σ v > vib ≈ 2 × 10 −10 cm 3 s −1 (Green 1986), we derive a critical density n cr ∼ 10 8 cm −3 . Critical densities of vibrationally excited states of other molecules typically tracing "hot cores" are comparably high, n cr > 10 9 cm −3 (Wyrowski et al 1998).…”

Section: Excitation Conditions Throughout Core A1mentioning

confidence: 99%

The feedback of an HC HII region on its parental molecular core

Moscadelli

Rivilla

Cesaroni

et al. 2018

A&A

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Context. G24.78+0.08 is a well known high-mass star-forming region, where several molecular cores harboring OB young stellar objects are found inside a clump of size ≈1 pc. This article focuses on the most prominent of these cores, A1, where an intense hypercompact (HC) HII region has been discovered by previous observations. Aims. Our aim is to determine the physical conditions and the kinematics of core A1, and study the interaction of the HII region with the parental molecular core. Methods. We combine ALMA 1.4 mm high-angular resolution (≈0.′′2) observations of continuum and line emission with multi-epoch Very Long Baseline Interferometry data of water 22 GHz and methanol 6.7 GHz masers. These observations allow us to study the gas kinematics on linear scales from 10 to 104 au, and to accurately map the physical conditions of the gas over core A1. Results. The 1.4 mm continuum is dominated by free-free emission from the intense HC HII region (size ≈1000 au) observed to the North of core A1 (region A1N). Analyzing the H30α line, we reveal a fast bipolar flow in the ionized gas, covering a range of LSR velocities (VLSR) of ≈60 km s−1. The amplitude of the VLSR gradient, 22 km s−1 mpc−1, is one of the highest so far observed towards HC HII regions. Water and methanol masers are distributed around the HC HII region in A1N, and the maser three-dimensional (3D) velocities clearly indicate that the ionized gas is expanding at high speed (≥200 km s−1) into the surrounding molecular gas. The temperature distribution (in the range 100–400 K) over core A1, traced with molecular (CH3OCHO, 13CH3CN, 13CH3OH, and CH3CH2CN) transitions with level energy in the range 30 K ≤ Eu/k ≤ 300 K, reflects the distribution of shocks produced by the fast-expansion of the ionized gas of the HII region. The high-energy (550 K ≤ Eu/k ≤ 800 K) transitions of vibrationally excited CH3CN are likely radiatively pumped, and their rotational temperature can significantly differ from the kinetic temperature of the gas. Over core A1, the VLSR maps from both the 1.4 mm molecular lines and the 6.7 GHz methanol masers consistently show a VLSR gradient (amplitude ≈0.3 km s−1 mpc−1) directed approximately S–N. Rather than gravitationally supported rotation of a massive toroid, we interpret this velocity gradient as a relatively slow expansion of core A1.

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Section: Excitation Conditions Throughout Core A1mentioning

confidence: 99%

The feedback of an HC HII region on its parental molecular core

Moscadelli

Rivilla

Cesaroni

et al. 2018

A&A

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“…The lowest excited vibrational state of CH 3 CN is the doubly degenerate CCN bending mode 8 = 1 at a vibrational energy of 365.0 cm −1 [33]. It was studied first in 1961 by rotational spectroscopy between 92 and 222 GHz (J = 4 to 11) [34].…”

Section: Introductionmentioning

confidence: 99%

Rotational spectroscopy as a tool to investigate interactions between vibrational polyads in symmetric top molecules: Low-lying states v8⩽2 of methyl cyanide, CH3CN

Müller

Brown

Drouin

et al. 2015

Journal of Molecular Spectroscopy

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Rotational and rovibrational spectra of methyl cyanide were recorded to analyze interactions in low-lying vibrational states and to construct line lists for radio astronomical observations in space as well as for infrared spectroscopic investigations of planetary atmospheres. The rotational spectra cover large portions of the 36−1627 GHz region. In the infrared (IR), a spectrum was recorded for this study in the region of 2ν 8 around 717 cm −1 with assignments covering 684−765 cm −1. Additional spectra in the ν 8 region were used to validate the analysis. Information on the K level structure of CH 3 CN is almost exclusively obtained from IR spectra, as are basics of the J level structure. The large amount and the high accuracy of the rotational data improves knowledge of the J level structure considerably. Moreover, since these data extend to much higher J and K quantum numbers, they allowed us to investigate for the first time in depth local interactions between these states which occur at high K values. In particular, we have detected several interactions between 8 = 1 and 2. Notably, there is a strong ∆ 8 = ±1, ∆K = 0, ∆l = ±3 Fermi resonance between 8 = 1 −1 and 8 = 2 +2 at K = 14. Pronounced effects in the spectrum are also caused by resonant ∆ 8 = ±1, ∆K = ∓2, ∆l = ±1 interactions between 8 = 1 and 2 at K = 13, l = −1/K = 11, l = 0 and at K = 15, l = +1/K = 13, l = +2. An equivalent resonant interaction occurs between K = 14 of the ground vibrational state and K = 12, l = +1 of 8 = 1 for which we present the first detailed account. A preliminary account was given in an earlier study on the ground vibrational state. Similar resonances were found for CH 3 CCH and, more recently, for CH 3 NC, warranting comparison of the results. From data pertaining to 8 = 2, we also investigated rotational interactions with 4 = 1 as well as ∆ 8 = ±1, ∆K = 0, ∆l = ±3 Fermi interactions between 8 = 2 and 3. We have derived N 2-and self-broadening coefficients for the ν 8 , 2ν 8 − ν 8 , and 2ν 8 bands from previously determined ν 4 values. Subsequently, we determined transition moments and intensities for the three IR bands.

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“…The ν 8 transition frequencies were taken from Koivusaari [480] , and the 2 ν 8 transition frequencies were from Müller et al [479] .…”

Section: Ch 3 Cn (Molecule 41)mentioning

confidence: 99%