261 research outputs found
Experimental Confirmation of Quantum Monodromy: The Millimeter Wave Spectrum of Cyanogen Isothiocyanate NCNCS
We have made energy-momentum maps for the experimental end-over-end rotational energy and the two-dimensional bending vibrational energy, both of which confirm the dominating effects of nontrivial quantum monodromy in cyanogen isothiocyanate. Accidental resonances in the rotational spectra yield accurate intervals between bending states
A simple approach to the correlation of rotovibrational states in four-atomic molecules
The problem of correlation between quantum states of four-atomic molecules in
different geometrical configurations is reviewed in detail. A general, still
simple rule is obtained which allows one to correlate states of a linear
four-atomic molecule with those of any kind of non-linear four-atomic molecule.Comment: 16 pages (+8 figures), Postscript (ready to print!
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Notations and conventions in molecular spectroscopy: part 1. General spectroscopic notation
The field of Molecular Spectroscopy was surveyed in order to determine a set of
conventions and symbols which are in common use in the spectroscopic literature. This
document, which is Part I in a series, establishes the notations and conventions used for
general spectroscopic notations and deals with quantum mechanics, quantum numbers
(vibrational states, angular momentum and energy levels), spectroscopic transitions, and
miscellaneous notations (e.g. spectroscopic terms). Further parts will follow, dealing inter
alia with symmetry notation, permutation and permutation-inversion symmetry notation,
vibration-rotation spectroscopy and electronic spectroscopy
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Notations and conventions in molecular spectroscopy: part 2. Symmetry notation
The field of Molecular Spectroscopy was surveyed in order to determine a set of
conventions and symbols which are in common use in the spectroscopic literature. This
document, which is Part 2 in a series, establishes the notations and conventions used for the
description of symmetry in rigid molecules, using the Schoenflies notation. It deals firstly
with the symmetry operators of the molecular point groups (also drawing attention to the
difference between symmetry operators and elements). The conventions and notations of the
molecular point groups are then established, followed by those of the representations of these
groups as used in molecular spectroscopy. Further parts will follow, dealing inter alia with
permutation and permutation-inversion symmetry notation, vibration-rotation spectroscopy
and electronic spectroscopy
A Pre-Protostellar Core in L1551
Large field surveys of NH3, C2S, 13CO and C18O in the L1551 dark cloud have
revealed a prolate, pre-protostellar molecular core (L1551-MC) in a relatively
quiescent region to the northwest of the well-known IRS 5 source. The kinetic
temperature is measured to be 9K, the total mass is ~2Msun, and the average
particle density is 10^4-10^5 cm^(-3). L1551-MC is 2.25' x 1.11' in projection
oriented at a position angle of 133deg. The turbulent motions are on the order
of the sound speed in the medium and contain 4% of the gravitational energy,
E_{grav}, of the core. The angular momentum vector is projected along the major
axis of L1551-MC corresponding to a rotational energy of 2.5E-3(sin
i)^(-2)|E_{grav}|. The thermal energy constitutes about a third of |E_{grav}|
and the virial mass is approximately equal to the total mass. L1551-MC is
gravitationally bound and in the absence of strong, ~160 microgauss, magnetic
fields will likely contract on a ~0.3 Myr time scale. The line profiles of many
molecular species suggest that the cold quiescent interior is surrounded by a
dynamic, perhaps infalling envelope which is embedded within the ambient
molecular gas of L1551.Comment: 27 pages, 7 figures, ApJ accepte
Detection of FeO towards SgrB2
We have observed the J=5-4 ground state transition of FeO at a frequency of
153 GHz towards a selection of galactic sources.
Towards the galactic center source SgrB2, we see weak absorption at
approximately the velocity of other features towards this source (62 km
s LSR).
Towards other sources, the results were negative as they were also for
MgOH(3-2) and FeC(6-5). We tentatively conclude that the absorption seen toward
SgrB2 is due to FeO in the hot ( 500 K) relatively low density absorbing
gas known to be present in this line of sight.
This is the first (albeit tentative) detection of FeO or any iron--containing
molecule in the interstellar gas. Assuming the observed absorption to be due to
FeO, we estimate [FeO]/[SiO] to be of order or less than 0.002 and
[FeO]/[H] of order . This is compatible with our negative
results in other sources.
Our results suggest that the iron liberated from grains in the shocks
associated with SgrB2 remains atomic and is not processed into molecular form.Comment: 1 postscrit figure,10 page
Rotational cooling of molecules using lamps
We investigate theoretically the application of tailored incoherent
far-infrared fields in combination with laser excitation of a single
rovibrational transition for rotational cooling of translationally cold polar
diatomic molecules. The cooling schemes are effective on a timescale shorter
than typical unperturbed trapping times in ion traps and comparable to
obtainable confinement times of neutral molecules.Comment: 5 pages, 2 figure
Rotational spectra of isotopic species of methyl cyanide, CHCN, in their ground vibrational states up to terahertz frequencies
Methyl cyanide is an important trace molecule in star-forming regions. It is
one of the more common molecules used to derive kinetic temperatures in such
sources. As preparatory work for Herschel, SOFIA, and in particular ALMA we
want to improve the rest frequencies of the main as well as minor isotopologs
of methyl cyanide. The laboratory rotational spectrum of methyl cyanide in
natural isotopic composition has been recorded up to 1.63 THz. Transitions with
good signal-to-noise ratio could be identified for CHCN, CHCN,
CHCN, CHCN, CHDCN, and CHCN in their
ground vibrational states up to about 1.2 THz. The main isotopic species could
be identified even in the highest frequency spectral recordings around 1.6 THz.
The highest quantum numbers included in the fit are 64 for
CHCN and 89 for the main isotopic species. Greatly improved
spectroscopic parameters have been obtained by fitting the present data
together with previously reported transition frequencies. The present data will
be helpful to identify isotopologs of methyl cyanide in the higher frequency
bands of instruments such as the recently launched Herschel satellite, the
upcoming airplane mission SOFIA or the radio telescope array ALMA.Comment: 13 pages, 2 figures, article appeared; CDMS links update
Study of Photon Dominated Regions in Cepheus B
Aim: The aim of the paper is to understand the emission from the photon
dominated regions in Cepheus B, estimate the column densities of neutral carbon
in bulk of the gas in Cepheus B and to derive constraints on the factors which
determine the abundance of neutral carbon relative to CO. Methods: This paper
presents 15'x15' fully sampled maps of CI at 492 GHz and 12CO 4-3 observed with
KOSMA at 1' resolution. The new observations have been combined with the FCRAO
12CO 1-0, IRAM-30m 13CO 2-1 and C18O 1-0 data, and far-infrared continuum data
from HIRES/IRAS. The KOSMA-tau spherical PDR model has been used to understand
the CI and CO emission from the PDRs in Cepheus B and to explain the observed
variation of the relative abundances of both C^0 and CO. Results: The emission
from the PDR associated with Cepheus B is primarily at V_LSR between -14 and
-11 km s^-1. We estimate about 23% of the observed CII emission from the
molecular hotspot is due to the ionized gas in the HII region. Over bulk of the
material the C^0 column density does not change significantly, (2.0+-1.4)x10^17
cm^-2, although the CO column density changes by an order of magnitude. The
observed \cbyco abundance ratio varies between 0.06 and 4 in Cepheus B. We find
an anti-correlation of the observed C/CO abundance ratio with the observed
hydrogen column density, which holds even when all previous observations
providing C/CO ratios are included. Here we show that this observed variation
of C/CO abundance with total column density can be explained only by clumpy
PDRs consisting of an ensemble of clumps. At high H2 column densities high mass
clumps, which exhibit low C/CO abundance, dominate, while at low column
densities, low mass clumps with high C/CO abundance dominate.Comment: 12 pages, 10 figures, Accepted for publication in A&
Atomic Carbon in M82: Physical conditions derived from simultaneous observations of the [CI] fine structure submillimeter wave transitions
We report the first extragalactic detection of the neutral carbon [CI]
3P2-3P1 fine structure line at 809 GHz. The line was observed towards M82
simultaneously with the 3P1-3P0 line at 492 GHz, providing a precise
measurement of the J=2-1/J=1-0 integrated line ratio of 0.96 (on a [K km s^-1]
-scale). This ratio constrains the [CI] emitting gas to have a temperature of
at least 50 K and a density of at least 10^4 cm^-3. Already at this minimum
temperature and density, the beam averaged CI-column density is large, 2.1
10^18 cm^-2, confirming the high CI/CO abundance ratio of approximately 0.5
estimated earlier from the 492 GHz line alone. We argue that the [CI] emission
from M82 most likely arises in clouds of linear size around a few pc with a
density of about 10^4 cm^-3 or slightly higher and temperatures of 50 K up to
about 100 K.Comment: 4 pages, 2 figures, ApJL in press, postscript also available at
ftp://apollo.ph1.uni-koeln.de/pub/stutzki/m82_pap.ps.gz
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