J/MNRAS/546/F2055 Collisional dynamics of NC4NH+ with H2 (Chahal+, 2026)
Collisional dynamics of NC4NH+ with H2 in the interstellar medium.
Chahal P., Kumar T.J.D.
<Mon. Not. R. Astron. Soc. 546, staf2055 (2026)>
=2026MNRAS.546f2055C 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 (NC4NH+) in collision with both para- and
ortho-H2 over the temperature range 1-100K. Such low-temperature
collisions help determine the state-to-state rate coefficients for the
rotational transitions of NC4NH+, a recently detected species in
TMC-1. To study these collisions, a four-dimensional (4D) ab initio
potential energy surface (PES) for the NC4NH+-H2 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-H2.
Description:
In the present paper, we have reported the low-temperature rotational
dynamical study of protonated dicyanoacetylene (NC4NH+) with H2,
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 NC4NH^+
van der Waals complex has a global minimum located at phi=0°,
theta2=90°. theta1=0°. and R=5.8Å 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:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
pes.dat 26 1792021 Potential energy surface (PES) data for the
collision of NC4NH+ with H2
ortho.dat 336 100 Rate coefficients for the collision of
NC4NH+ with ortho - H2
para.dat 336 100 Rate coefficients for the collision of
NC4NH+ with para - H2
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Byte-by-byte Description of file: pes.dat
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Bytes Format Units Label Explanations
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1- 4 F4.1 0.1nm R Distance between the centre of mass of
NC4NH+ and H2
6- 7 I2 deg phi Dihedral angle between the NC_4NH^+ molecule
and H2
9- 11 I3 deg theta2 Rotation of H2 molecule
13- 15 I3 deg theta1 Rotation of NC4NH+ molecule
17- 26 E10.5 cm-1 E Energy which is obtained as a result
of NC4NH+ - H2 collision
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Byte-by-byte Description of file: ortho.dat para.dat
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Bytes Format Units Label Explanations
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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
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Acknowledgements:
Pooja Chahal, pooja.21cyz0014(at)iitrpr.ac.in
(End) Patricia Vannier [CDS] 14-Nov-2025