Quantum Scattering Study of <scp>NCCNH</scp> ⁺ ‐ <scp> H ₂ </scp> Collision Under Interstellar Conditions

The rotational dynamics of protonated cyanogen (NCCNH⁺) is studied for collision with both para (p-) and ortho (o-) hydrogen (H₂) in the temperature range <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics><mml:mrow><mml:mn>1</mml:mn> <mml:mo>-</mml:mo> <mml:mn>100</mml:mn></mml:mrow> <mml:annotation>$$ 1-100 $$</mml:annotation></mml:semantics> </mml:math> K. Such cold collisions with H₂ are essential to get state-to-state rate coefficients for rotational transitions of newly detected NCCNH⁺. First, the ab initio 4D potential energy surface (PES) for NCCNH⁺-H₂ collision is generated at CCSD(T)-F12b level of theory using augmented triple zeta basis, considering rigid rotor approximation. The 4D PES is further fitted into a neural network (NN) model to augment the PES by <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics><mml:mrow><mml:mo>∼</mml:mo> <mml:mn>130</mml:mn></mml:mrow> <mml:annotation>$$ \sim 130 $$</mml:annotation></mml:semantics> </mml:math> folds. The PES is then expanded using bispherical harmonics functions to get radial terms, which are expressed as analytic functions. The cross-sections and rate coefficients for NCCNH⁺ are calculated using the exact close-coupling method for rotational states up to <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics><mml:mrow><mml:mi>j</mml:mi> <mml:mo>=</mml:mo> <mml:mn>16</mml:mn></mml:mrow> <mml:annotation>$$ j=16 $$</mml:annotation></mml:semantics> </mml:math> , considering both p- and o-H₂ collisions. The rates show similar behavior to the earlier studied NCCN-H₂ collision, with the latter having larger rate coefficients.