Vol.:(0123456789) 1 3 Theoretical Chemistry Accounts (2020) 139:97 https://doi.org/10.1007/s00214-020-02606-y REGULAR ARTICLE Radiative association of P and Cl atoms Carmen Maria Andreazza 1  · Amaury Augusto de Almeida 2  · Gustavo Juliani Costa 3  · Antonio Carlos Borin 3 Received: 19 December 2019 / Accepted: 6 May 2020 / Published online: 30 May 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020 Abstract Thermal rate constants for the formation of PCl radical via radiative association have been estimated from potential energy curves and dipole moments calculated by accurate ab initio methods. The formation of PCl through radiative association of P( 4 S) and Cl( 2 P) atoms occurs mainly through the formation of a quasi-molecule in the A 3  state, which decays by an allowed dipole transition to the ground X 3  - state. The computed rate constant can be represented over the 300–5000 K temperature range in the form k(T )= 1.95 × 10 −20 (T ∕300) 0.605 exp(−1690∕T ) cm 3 s −1 and over the 5000–14,000 K temperature range by the relation k(T )= 8.53 × 10 −22 (T ∕300) 1.595 exp(−2.5∕T ) cm 3 s −1 , where T is in K. Keywords P + Cl reaction · PCl radical · Rate constant 1 Introduction Phosphorus plays a central role in the formation of the cel- lular membranes (phospholipids) and deoxyribonucleic acid (DNA), and it serves to store metabolic energy as ATP (adenosine triphosphate) [1]. In turn, chlorine is found in amino acids, steroids and fatty acids [2]. Cl is also needed for maintaining the correct osmotic pressure of cells and for nervous system [3]. The former has only one stable iso- tope: 31 P, and the later has two: 35 Cl and 37 Cl. Phosphorus and chlorine are thought to be mainly synthesized in mas- sive stars, before and during supernova explosions [4–6]. 37 Cl and 31 P can also be formed during the asymptotic giant branch (AGB) phase of low mass stars [7, 8]. Chlorine and phosphorus have a relatively low cosmic abundance of 3.2 × 10 -7 and 2.6 × 10 -7 , relative to hydro- gen, respectively, that are 2–3 orders of magnitude smaller than those of carbon, nitrogen and oxygen [9]. Despite this fact, several P-containing species have been identifed in the inner envelope of evolved stars, including CP, PO, PN, HCP, CCP and PH 3 [10–15]. PN and HCP have also been observed in the envelope of proto-planetary nebula CRL 2688 [14]. In star forming regions, only PN and PO are observed [16, 17]. PH 3 has also been observed in the upper atmospheres of Jupiter and Saturn [18]. In turn, chlorine-bearing com- pounds, including HCl, NaCl, AlCl, KCl, have been identi- fed in the innermost layers of the circumstellar envelope of evolved stars [19, 20]. HCl is also abundant in cool stars [21] and in sunspot umbrae [22]. NaCl has also been observed toward the proto-planetary nebula CRL 2688 [23] and in the atmosphere of Io [24]. The frst detection of HCl in dense interstellar clouds has been reported by Blake et al. [25]. Subsequently, this species was detected toward the difuse clouds [26] and in the coma of comet 67P/Churyumov–Ger- asimenko [27]. In addition, HCl + , chloronium ion H 2 Cl + and para-chloronium ions have been detected in star forming regions [28–30]. These compounds have also been found in extragalactic sources at redshifts of 0.89 and 0.68 [31, 32]. The most recent observation of a chlorine-bearing species is that of CH 3 Cl in the young stellar object IRAS 16293-2422 “Festschrift in honor of Prof. Fernando R. Ornellas” Guest Edited by Adélia Justino Aguiar Aquino, Antonio Gustavo Sampaio de Oliveira Filho & Francisco Bolivar Correto Machado. * Antonio Carlos Borin ancborin@iq.usp.br Carmen Maria Andreazza cm.andreazza@unesp.br Amaury Augusto de Almeida amaury.almeida@iag.usp.br 1 DEMAC, IGCE, Universidade Estadual Paulista, Av. 24A, 1515, Rio Claro, SP CEP 13506-700, Brazil 2 Department of Astronomy, IAG, Universidade de São Paulo, Rua do Matão, 1226, São Paulo, SP CEP 05508-090, Brazil 3 Department of Fundamental Chemistry, Institute of Chemistry, University of São Paulo, Avenida Professor Lineu Prestes, 748, São Paulo, SP CEP 05508-000, Brazil