7 research outputs found
The BX electronic origin band of CH
The rotationally resolved spectrum of the BX electronic origin
band transition of CH is presented. The spectrum is recorded using
cavity ring-down spectroscopy in combination with supersonic plasma jets by
discharging a CH/He/Ar gas mixture. A detailed analysis of more
than a hundred fully-resolved transitions allows for an accurate determination
of the spectroscopic parameters for both the ground and electronically excited
state of CH.Comment: 4 pages, 1 figure, 2 table
C and the Diffuse Interstellar Bands: An Independent Laboratory Check
In 2015, Campbell et al. (Nature 523, 322) presented spectroscopic laboratory
gas phase data for the fullerene cation, C, that coincide with
reported astronomical spectra of two diffuse interstellar band (DIB) features
at 9633 and 9578 \AA. In the following year additional laboratory spectra were
linked to three other and weaker DIBs at 9428, 9366, and 9349 \AA. The
laboratory data were obtained using wavelength-dependent photodissociation
spectroscopy of small (up to three) He-tagged CHe ion complexes,
yielding rest wavelengths for the bare C cation by correcting for the
He-induced wavelength shifts. Here we present an alternative approach to derive
the rest wavelengths of the four most prominent C absorption features,
using high resolution laser dissociation spectroscopy of C embedded in
ultracold He droplets. Accurate wavelengths of the bare fullerene cation are
derived based on linear wavelength shifts recorded for HeC species
with up to 32. A careful analysis of all available data results in precise
rest wavelengths (in air) for the four most prominent C bands:
9631.9(1) \AA, 9576.7(1) \AA, 9427.5(1) \AA, and 9364.9(1) \AA. The
corresponding band widths have been derived and the relative band intensity
ratios are discussed
A Spectroscopic Survey of Electronic Transitions of CH, CH, and CD
Electronic spectra of CH are measured in the cm
domain using cavity ring-down spectroscopy of a supersonically expanding
hydrocarbon plasma. In total, 19 (sub)bands of CH are presented, all
probing the vibrational manifold of the B electronically excited state.
The assignments are guided by electronic spectra available from matrix
isolation work, isotopic substitution experiments (yielding also spectra for
CH and CD), predictions from ab initio calculations as well as
rotational fitting and vibrational contour simulations using the available
ground state parameters as obtained from microwave experiments. Besides the
origin band, three non-degenerate stretching vibrations along the
linear backbone of the CH molecule are assigned: the mode
associated with the C-C bond vibration and the and modes
associated with CC triple bonds. For the two lowest and
bending modes, a Renner-Teller analysis is performed identifying the
() and both () and
() components. In addition, two higher lying bending
modes are observed, which are tentatively assigned as ()
and () levels. In the excitation region below the first
non-degenerate vibration (), some transitions are
observed that are assigned as even combination modes of low-lying bending
vibrations. The same holds for a transition found above the
level. From these spectroscopic data and the vibronic analysis a
comprehensive energy level diagram for the B state of CH is derived
and presented.Comment: Accepted for publication in The Journal of Physical Chemistry A (26
July 2016
Spectroscopic Survey of Electronic Transitions of C<sub>6</sub>H, <sup>13</sup>C<sub>6</sub>H, and C<sub>6</sub>D
Electronic spectra of C<sub>6</sub>H are measured in the 18âŻ950â21âŻ100
cm<sup>â1</sup> domain using cavity ring-down spectroscopy
of a supersonically expanding hydrocarbon plasma. In total, 19 (sub)Âbands
of C<sub>6</sub>H are presented, all probing the vibrational manifold
of the B<sup>2</sup>Î electronically excited state. The assignments
are guided by electronic spectra available from matrix isolation work,
isotopic substitution experiments (yielding also spectra for <sup>13</sup>C<sub>6</sub>H and C<sub>6</sub>D), predictions from <i>ab initio</i> calculations, and rotational fitting and vibrational
contour simulations using the available ground state parameters as
obtained from microwave experiments. Besides the 0<sub>0</sub><sup>0</sup> origin band, three nondegenerate
stretching vibrations along the linear backbone of the C<sub>6</sub>H molecule are assigned: the ν<sub>6</sub> mode associated
with the CâC bond vibration and the ν<sub>4</sub> and
ν<sub>3</sub> modes associated with CîźC triple bonds.
For the two lowest ν<sub>11</sub> and ν<sub>10</sub> bending
modes, a RennerâTeller analysis is performed identifying the
Îź<sup>2</sup>ÎŁÂ(ν<sub>11</sub>) and both Îź<sup>2</sup>ÎŁÂ(ν<sub>10</sub>) and Îş<sup>2</sup>ÎŁÂ(ν<sub>10</sub>) components. In addition, two higher lying bending modes
are observed, which are tentatively assigned as Îź<sup>2</sup>ÎŁÂ(ν<sub>9</sub>) and Îź<sup>2</sup>ÎŁÂ(ν<sub>8</sub>) levels. In the excitation region below the first nondegenerate
vibration (ν<sub>6</sub>), some <sup>2</sup>Î â<sup>2</sup>Î transitions are observed that are assigned as even
combination modes of low-lying bending vibrations. The same holds
for a <sup>2</sup>Î <sup>2</sup>Î transition found above
the ν<sub>6</sub> level. From these spectroscopic data and the
vibronic analysis a comprehensive energy level diagram for the B<sup>2</sup>Î state of C<sub>6</sub>H is derived and presented
The EDIBLES survey
We report cosmic ray ionization rates toward ten reddened stars studied within the framework of the EDIBLES (ESO Diffuse Interstellar Bands Large Exploration Survey) program, using the VLT-UVES. For each sightline, between two and ten individual rotational lines of OH+ have been detected in its (0,0) and (1,0) A3Î â X3ÎŁâ electronic band system. This allows constraining of OH+ column densities toward different objects. Results are also presented for 28 additional sightlines for which only one or rather weak signals are found. An analysis of these data makes it possible to derive the primary cosmic ray ionization rate Îśp in the targeted diffuse interstellar clouds. For the ten selected targets, we obtain a range of values for Îśp equal to (3.9â16.4) Ă 10â16Â sâ1. These values are higher than the numbers derived in previous detections of interstellar OH+ in the far-infrared/submillimeter-wave regions and in other near-ultraviolet studies. This difference is a result of using new OH+ oscillator strength values and a more complete picture of all relevant OH+ formation and destruction routes (including the effect of proton recombinations on PAHs), and the relatively high N(OH+) seen toward those ten targets