Engineering topics

Schlemmer, Stephan

Publications and source records attributed to Schlemmer, Stephan.

6 records

DOE OSTI2019

Controlling internal degrees: general discussion

Temperature is a very important concept in ion spectroscopy and its control has seen tremendous advances in recent years. Cryogenic ion traps are now found in many experiments and serve as thermostats, reaction vessels, clustering sources and spectroscopic sample chambers. The control over internal degrees of freedom provides routes to forming ions that are relevant at cryogenic temperatures such as in the interstellar medium and to control and lock-in conformations. It also provides a condensing environment and allows weakly bound clusters to be formed, which in turn provides new routes to action spectroscopy. This session will discuss the most recent developments in cryogenic spectroscopy and the research it enables and how new theoretical methods allow the prediction of experimental spectra as a function of temperature. The main discussion topics will cover: the best cooling methods; how temperature can be used to form exotic clusters and weakly interacting systems; and the possibilities for probing conformational locking and metastable structures.

Ahmed, Musahid↗

DOE OSTI2019

Pushing resolution in frequency and time: general discussion

One of the most important aspects of spectroscopy in general is resolution: the higher it is, the more information can be attained. At one end, spectral resolution provides geometric and electronic structural information and insights into weak interactions such as hydrogen bonds. At the other end, temporal resolution provides insight into geometric and electronic structural dynamics. The aim of this session is to provide a forum to discuss the state of the art in terms of resolution in general and how recent advances in light sources and ion mass spectroscopy can be used to study unexplored phenomena and interactions. Theoretical developments also have a key role in this area, particularly in relation to time-resolved measurements, since theoretical predictions are of key importance for providing molecular-insight into the observed experimental dynamics. The key discussion points will revolve around how experiment and theory can best combine to achieve the deepest insight, both in terms of structure and dynamics; and how new light sources may open new horizons.

Simons, Jack↗

DOE OSTI2017

Accurate Frequency Determination of Vibration–Rotation and Rotational Transitions of SiH{sup +}

The fundamental {sup 28}SiH{sup +} ion has been characterized in a collaborative work, utilizing a hollow-cathode discharge laser spectrometer and a cryogenic ion trap spectrometer. Twenty-three vibration–rotation transitions around 4.75 μm have been detected with high accuracy. This has facilitated the first direct measurement of the pure rotational transition J=1←0 at 453056.3632(4) MHz in the trap spectrometer. The measured and accurately predicted transitions enable the search for this ion in space with IR and sub-mm telescopes.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2017

Detection of Interstellar Ortho-D{sub 2}H{sup +} with SOFIA

We report on the detection of the ground-state rotational line of ortho-D{sub 2}H{sup +} at 1.477 THz (203 μm) using the German REceiver for Astronomy at Terahertz frequencies (GREAT) on board the Stratospheric Observatory For Infrared Astronomy (SOFIA). The line is seen in absorption against far-infrared continuum from the protostellar binary IRAS 16293-2422 in Ophiuchus. The para-D{sub 2}H{sup +} line at 691.7 GHz was not detected with the APEX telescope toward this position. These D{sub 2}H{sup +} observations complement our previous detections of para-H{sub 2}D{sup +} and ortho-H{sub 2}D{sup +} using SOFIA and APEX. By modeling chemistry and radiative transfer in the dense core surrounding the protostars, we find that the ortho-D{sub 2}H{sup +} and para-H{sub 2}D{sup +} absorption features mainly originate in the cool (T < 18 K) outer envelope of the core. In contrast, the ortho-H{sub 2}D{sup +} emission from the core is significantly absorbed by the ambient molecular cloud. Analyses of the combined D{sub 2}H{sup +} and H{sub 2}D{sup +} data result in an age estimate of ∼5 × 10{sup 5} yr for the core, with an uncertainty of ∼2 × 10{sup 5} yr. The core material has probably been pre-processed for another 5 × 10{sup 5} years in conditions corresponding to those in the ambient molecular cloud. The inferred timescale is more than 10 times the age of the embedded protobinary. The D{sub 2}H{sup +} and H{sub 2}D{sup +} ions have large and nearly equal total (ortho+para) fractional abundances of ∼10{sup −9} in the outer envelope. This confirms the central role of H{sub 3}{sup +} in the deuterium chemistry in cool, dense gas, and adds support to the prediction of chemistry models that also D{sub 3}{sup +} should be abundant in these conditions.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2016

Unifying the rotational and permutation symmetry of nuclear spin states: Schur-Weyl duality in molecular physics

In modern physics and chemistry concerned with many-body systems, one of the mainstays is identical-particle-permutation symmetry. In particular, both the intra-molecular dynamics of a single molecule and the inter-molecular dynamics associated, for example, with reactive molecular collisions are strongly affected by selection rules originating in nuclear-permutation symmetry operations being applied to the total internal wavefunctions, including nuclear spin, of the molecules involved. We propose here a general tool to determine coherently the permutation symmetry and the rotational symmetry (associated with the group of arbitrary rotations of the entire molecule in space) of molecular wavefunctions, in particular the nuclear-spin functions. Thus far, these two symmetries were believed to be mutually independent and it has even been argued that under certain circumstances, it is impossible to establish a one-to-one correspondence between them. However, using the Schur-Weyl duality theorem we show that the two types of symmetry are inherently coupled. In addition, we use the ingenious representation-theory technique of Young tableaus to represent the molecular nuclear-spin degrees of freedom in terms of well-defined mathematical objects. This simplifies the symmetry classification of the nuclear wavefunction even for large molecules. Also, the application to reactive collisions is very straightforward and provides a much simplified approach to obtaining selection rules.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2014

LABORATORY ROTATIONAL SPECTRUM OF l-C{sub 3}H{sup +} AND CONFIRMATION OF ITS ASTRONOMICAL DETECTION

The rotational spectrum of l-C{sub 3}H{sup +} has been measured in the millimeter-wave band in a 4 K cryogenic ion trap apparatus employing a novel mass-selective action spectroscopy method based on light induced reactions (LIR). Line positions of four rotational transitions (J = 1-2 up to J = 4-5) were observed with a relative precision of 3 × 10{sup –7}. The experimental transition frequencies and derived spectroscopic constants agree with those from recent astronomical observations, and unambiguously confirm the detection of this astrochemically relevant carbocation in the Horsehead photodissociation region and toward Sgr B2(N)

74 ATOMIC AND MOLECULAR PHYSICS↗