Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Contact Ion Pairs of Phosphate Groups in Water -- Two-Dimensional
  Infrared Spectroscopy of Dimethyl-Phosphate and Ab-Initio Simulations   The interaction of phosphate groups with ions in an aqueous environment has a
strong impact on the structure and folding processes of DNA and RNA. The
dynamic variety of ionic arrangements, including both contact pairs and water
separated ions, and the molecular coupling mechanisms are far from being
understood. In a combined experimental and theoretical approach, we address the
properties of contact ion pairs of the prototypical system dimethyl-phosphate
with Na$^+$, Ca$^{2+}$, and Mg$^{2+}$ ions in water. Linear and femtosecond
two-dimensional infrared (2D-IR) spectroscopy of the asymmetric (PO$_2$)$^-$
stretching vibration separates and characterizes the different species via
their blue-shifted vibrational signatures and 2D-IR lineshapes.
Phosphate-magnesium contact pairs stand out as the most compact geometry while
the contact pairs with Ca$^{2+}$ and Na$^+$ display a wider structural
variation. Microscopic density functional theory simulations rationalize the
observed frequency shifts and reveal distinct differences between the contact
geometries.

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The categories of this paper are: dg-ga
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The categories of this paper are: funct-an
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The categories of this paper are: q-bio
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The categories of this paper are: atom-ph
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The categories of this paper are: hep-lat
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The categories of this paper are: cmp-lg
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The categories of this paper are: supr-con
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The categories of this paper are: mtrl-th
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The categories of this paper are: nucl-ex
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The categories of this paper are: bayes-an
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The categories of this paper are: adap-org
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The categories of this paper are: q-alg
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The categories of this paper are: acc-phys
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The categories of this paper are: alg-geom
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The categories of this paper are: math
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The categories of this paper are: q-fin