High-Temperature Line List of Phosphaethyne (HCP)

Abstract

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(X 1 Σ + ) using robust first-principles methods. The analytical potential energy surface and dipole moment surface were constructed based on 26478 ab initio points from coupledcluster 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 Jdependent 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 2v 2 and v 3 bands has been reproduced.