Carbon dioxide and propane nucleation: the emergence of a nucleation barrier

• Published in: Physical chemistry chemical physics : PCCP 2020-07, Vol.22 (28), p.15986-15998
• Main Authors: Krohn, Jan, Lippe, Martina, Li, Chenxi, Signorell, Ruth
• Format: Article
• Language: English
• Subjects: Carbon dioxide; Carrier gases; Clusters; Free energy; Gas pressure; Mass spectrometry; Nucleation; Quantum chemistry; Rate constants; Time dependence; Ultraviolet radiation
• ISSN: 1463-9076; 1463-9084
• DOI: 10.1039/d0cp01771j

We investigate homogeneous gas-phase nucleation of CO 2 and C 3 H 8 in the uniform postnozzle flow of Laval expansions in the temperature range of 31.2 K to 62.9 K and 32.0 K to 42.1 K, respectively. Time-dependent cluster size distributions are recorded with mass spectrometry after single-photon ionization with vacuum ultraviolet light. Net monomer-cluster forward rate constants and experimental nucleation rates J are retrieved from the time-dependent cluster size distributions. The comparison of experimental enhancement factors derived from these net forward rates with calculated enhancement factors provides an indication for the transition from barrier-limited to barrierless nucleation. Our data suggest such a transition for CO 2 , but not for C 3 H 8 . The values of J lie in the range from 9 × 10 14 cm −3 s −1 to 6 × 10 15 cm −3 s −1 . For CO 2 , the comparison of J with a modeled nucleation rate J QM based on quantum chemical calculations of the free energy barrier also hints at a transition from barrierless condensation to barrier-limited nucleation. Furthermore, we address the influence of the carrier gas pressure on the nucleation rate. A direct molecular level study of CO 2 and C 3 H 8 nucleation indicates a transition from barrierless to barrier-limited nucleation.