J/MNRAS/546/F2055 Collisional dynamics of NC_4_NH^+^ with H_2_ (Chahal+, 2026) ================================================================================ Collisional dynamics of NC_4_NH^+^ with H_2_ in the interstellar medium. Chahal P., Kumar T.J.D. =2026MNRAS.546f2055C (SIMBAD/NED BibCode) ================================================================================ ADC_Keywords: Atomic physics ; Interstellar medium Keywords: ISM: abundances - ISM: molecules - software: machine learning - techniques: spectroscopic Abstract: The present work explores the quantum dynamics of protonated dicyanoacetylene (NC_4_NH^+^) in collision with both para- and ortho-H_2_ over the temperature range 1-100K. Such low-temperature collisions help determine the state-to-state rate coefficients for the rotational transitions of NC_4_NH^+^, a recently detected species in TMC-1. To study these collisions, a four-dimensional (4D) ab initio potential energy surface (PES) for the NC_4_NH^+^-H_2_ system was developed using the CCSD(T)-F12b method with an augmented triple-zeta basis set under the rigid-rotor approximation. The PES was then augmented through a neural network (NN) fitting approach to get the dense data. It was further expanded in bispherical harmonics, for the radial coefficients to be expressed in analytical form. Based on these radial coefficients, state-to-state cross sections and rate coefficients were calculated using the exact close-coupling method for the rotational states considering to both para- and ortho-H_2_. Description: In the present paper, we have reported the low-temperature rotational dynamical study of protonated dicyanoacetylene (NC_4_NH^+^) with H_2_, the dominant collider in the ISM. An accurate four-dimensional ab initio PES was generated at the CCSD(T)-F12b/aug-cc-pVTZ high level of theory. The 4D PES was further augmented using NN method. The NC_4_NH^+ van der Waals complex has a global minimum located at phi=0{deg}, theta_2_=90{deg}. theta_1_=0{deg}. and R=5.8{AA} with a well depth of -1276.85cm^-1^. The NN fitted 4D PES is further expanded into bispherical harmonics and analytically fitted to obtain the radial coefficients. The isotropic term is found to be attractive with a well depth of -283.51cm^-1^. The radial terms will be further used as a input for close-coupling scattering calculations. File Summary: -------------------------------------------------------------------------------- FileName Lrecl Records Explanations -------------------------------------------------------------------------------- ReadMe 80 . This file pes.dat 26 1792021 Potential energy surface (PES) data for the collision of NC_4_NH^+^ with H_2_ ortho.dat 336 100 Rate coefficients for the collision of NC_4_NH^+^ with ortho - H_2_ para.dat 336 100 Rate coefficients for the collision of NC_4_NH^^+ with para - H_2_ -------------------------------------------------------------------------------- Byte-by-byte Description of file: pes.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1- 4 F4.1 0.1nm R Distance between the centre of mass of NC_4_NH^+^ and H_2_ 6- 7 I2 deg phi Dihedral angle between the NC_4NH^+ molecule and H_2_ 9- 11 I3 deg theta2 Rotation of H_2_ molecule 13- 15 I3 deg theta1 Rotation of NC_4_NH^+^ molecule 17- 26 E10.5 cm-1 E Energy which is obtained as a result of NC_4_NH^+^ - H_2_ collision -------------------------------------------------------------------------------- Byte-by-byte Description of file: ortho.dat para.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1- 3 I3 K T [1/100] Temperature 5- 12 E8.3 --- Tr1-0 Rate transition 1->0 14- 21 E8.3 --- Tr2-1 Rate transition 2->1 23- 30 E8.3 --- Tr3-2 Rate transition 3->2 32- 39 E8.3 --- Tr4-3 Rate transition 4->3 41- 48 E8.3 --- Tr5-4 Rate transition 5->4 50- 57 E8.3 --- Tr6-5 Rate transition 6->5 59- 66 E8.3 --- Tr7-6 Rate transition 7->6 68- 75 E8.3 --- Tr8-7 Rate transition 8->7 77- 84 E8.3 --- Tr9-8 Rate transition 9->8 86- 93 E8.3 --- Tr10-9 Rate transition 10->9 95-102 E8.3 --- Tr11-10 Rate transition 11->10 104-111 E8.3 --- Tr12-11 Rate transition 12->11 113-120 E8.3 --- Tr13-12 Rate transition 13->12 122-129 E8.3 --- Tr14-13 Rate transition 14->13 131-138 E8.3 --- Tr15-14 Rate transition 15->14 140-147 E8.3 --- Tr16-15 Rate transition 16->15 149-156 E8.3 --- Tr17-16 Rate transition 17->16 158-165 E8.3 --- Tr18-17 Rate transition 18->17 167-174 E8.3 --- Tr19-18 Rate transition 19->18 176-183 E8.3 --- Tr2-0 Rate transition 2->0 185-192 E8.3 --- Tr3-1 Rate transition 3->1 194-201 E8.3 --- Tr4-2 Rate transition 4->2 203-210 E8.3 --- Tr5-3 Rate transition 5->3 212-219 E8.3 --- Tr6-4 Rate transition 6->4 221-228 E8.3 --- Tr7-5 Rate transition 7->5 230-237 E8.3 --- Tr8-6 Rate transition 8->6 239-246 E8.3 --- Tr9-7 Rate transition 9->7 248-255 E8.3 --- Tr10-8 Rate transition 10->8 257-264 E8.3 --- Tr11-9 Rate transition 11->9 266-273 E8.3 --- Tr12-10 Rate transition 12->10 275-282 E8.3 --- Tr13-11 Rate transition 13->11 284-291 E8.3 --- Tr14-12 Rate transition 14->12 293-300 E8.3 --- Tr15-13 Rate transition 15->13 302-309 E8.3 --- Tr16-14 Rate transition 16->14 311-318 E8.3 --- Tr17-15 Rate transition 17->15 320-327 E8.3 --- Tr18-16 Rate transition 18->16 329-336 E8.3 --- Tr19-17 Rate transition 19->17 -------------------------------------------------------------------------------- Acknowledgements: Pooja Chahal, pooja.21cyz0014(at)iitrpr.ac.in ================================================================================ (End) Patricia Vannier [CDS] 14-Nov-2025