High-Temperature Line List of Phosphaethyne (HCP)

Phosphaethyne (HCP) has been detected
in circumstellar
envelopes;
its spectroscopic line list is helpful for modeling the relevant atmospheric
opacity. We present the first comprehensive line list for HCP(X1Σ+) using robust first-principles methods.
The analytical potential energy surface and dipole moment surface
were constructed based on 26478 ab initio points
from coupled-cluster calculations, along with the considerations of
core–valence electron correlation and scalar relativistic effects.
The variational nuclear motion program TROVE was used to obtain the
ro-vibrational energy levels, Einstein A coefficients,
and so on. The J-dependent Coriolis-decoupled Hamiltonian
was adopted in the variational calculations with k ≤ 20, and the linear molecule treatment was applied to consider
the l-type doubling of the bending vibration. The
line list contains almost 0.45 billion transitions between 1.21 million
levels with rotational excitation up to J = 200.
It covers the wavenumber range of 0–9000 cm–1 (wavelengths above 1.11 μm) and is suitable for temperatures
up to 3000 K. The millimeter wave spectra agree well with the experiments,
and the Fermi resonance between 2v2 and v3 bands has been reproduced.