17 research outputs found
Coupled Blind Signal Separation and Spectroscopic Database Fitting of the Mid Infrared PAH Features
The aromatic infrared bands (AIBs) observed in the mid infrared spectrum are
attributed to Polycyclic Aromatic Hydrocarbons (PAHs). We observe the NGC
7023-North West (NW) PDR in the mid-infrared (10 - 19.5 micron) using the
Infrared Spectrometer (IRS), on board Spitzer. Clear variations are observed in
the spectra, most notably the ratio of the 11.0 to 11.2 micron bands, the peak
position of the 11.2 and 12.0 micron bands, and the degree of asymmetry of the
11.2 micron band. The observed variations appear to change as a function of
position within the PDR. We aim to explain these variations by a change in the
abundances of the emitting components of the PDR. A Blind Signal Separation
(BSS) method, i.e. a Non-Negative Matrix Factorization algorithm is applied to
separate the observed spectrum into components. Using the NASA Ames PAH IR
Spectroscopic Database, these extracted signals are fit. The observed signals
alone were also fit using the database and these components are compared to the
BSS components. Three component signals were extracted from the observation
using BSS. We attribute the three signals to ionized PAHs, neutral PAHs, and
Very Small Grains (VSGs). The fit of the BSS extracted spectra with the PAH
database further confirms the attribution to ionized and neutral PAHs and
provides confidence in both methods for producing reliable results. The 11.0
micron feature is attributed to PAH cations while the 11.2 micron band is
attributed to neutral PAHs. The VSG signal shows a characteristically
asymmetric broad feature at 11.3 micron with an extended red wing. By combining
the NASA Ames PAH IR Spectroscopic Database fit with the BSS method, the
independent results of each method can be confirmed and some limitations of
each method are overcome
Roadmap on dynamics of molecules and clusters in the gas phase
This roadmap article highlights recent advances, challenges and future prospects in studies of the dynamics of molecules and clusters in the gas phase. It comprises nineteen contributions by scientists with leading expertise in complementary experimental and theoretical techniques to probe the dynamics on timescales spanning twenty order of magnitudes, from attoseconds to minutes and beyond, and for systems ranging in complexity from the smallest (diatomic) molecules to clusters and nanoparticles. Combining some of these techniques opens up new avenues to unravel hitherto unexplored reaction pathways and mechanisms, and to establish their significance in, e.g. radiotherapy and radiation damage on the nanoscale, astrophysics, astrochemistry and atmospheric science
Low-Temperature Reactivity of C2n+1N- Anions with Polar Molecules
International audienceFollowing the recent discovery of molecular anions in the interstellar medium, we report on the kinetics of proton transfer reactions between cyanopolyynide anions C2n+1N- (n = 0, 1, 2) and formic acid HCOOH. The results, obtained from room temperature down to 36 K by means of uniform supersonic flows, show a surprisingly weak temperature dependence of the CN- reaction rate, in contrast with longer chain anions. The CN- + HCOOH reaction is further studied theoretically via a reduced dimensional quantum model that highlights a tendency of the reaction probability to decrease with temperature, in agreement with experimental data but at the opposite of conventional long-range capture theories. In return, comparing HCOOH to HC3N as target molecules suggests that dipole-dipole interactions must play an active role in overcoming this limiting effect at low temperatures. This work provides new fundamental insights on prototypical reactions between polar anions and polar molecules along with critical data for astrochemical modeling. © 2016 American Chemical Society