A Variationally Computed T = 300 K Line List for NH₃

Abstract

Calculations are reported on the rotation-vibration energy levels of ammonia with associated transition intensities. A potential energy surface obtained from coupled cluster CCSD(T) calculations and subsequent fitting against experimental data is further refined by a slight adjustment of the equilibrium geometry, which leads to a significant improvement in the rotational energy level structure. A new accurate ab initio dipole moment surface is determined at the frozen core CCSD(T)/aug-cc-pVQZ level. The calculation of an extensive ammonia line list necessitates a number of algorithmic improvements in the program TROVE that is used for the variational treatment of nuclear motion. Rotation-vibration transitions for (14)NH(3) involving states with energies up to 12,000 cm(-1) and rotational quantum number J = 20 are calculated. This gives 3.25 million transitions between 184,400 energy levels. Comparisons show good agreement with data in the HITRAN database but suggest that HITRAN is missing significant ammonia absorptions, particularly in the near-infrared.

First theoretical global line lists of ethylene (12C2H4) spectra for the temperature range 50−700 K in the far-infrared for quantification of absorption and emission in planetary atmospheres

“…A breakthrough in predicting rotationally resolved spectra of small molecules was made possible by accurate electronic structure calculations of the molecular PESs and DMSs (see, e.g., Partridge & Schwenke 1997;Cours et al 2002;Yurchenko et al 2009;Nikitin et al 2009;Lodi et al 2011;Császár et al 2010;Szalay et al 2011;Huang et al 2011aHuang et al , 2012Sousa-Silva et al 2014;Nikitin et al 2014;Li et al 2014;Delahaye et al 2015) and by developing efficient methods for quantum nuclear motion calculations (see Schwenke & Partridge 2001;Schwenke 2002;Cassam-Chenaï et al 2012;Yurchenko et al 2007;Wang & Carrington Jr. 2013a,b;Carter et al 2009;Rey et al 2012;Bowman et al 2005). In case of triatomics, such as water isotopic species (Yurchenko et al 2009;Barber et al 2011), carbon dioxide (Huang et al 2013(Huang et al , 2014, and ozone accurate theoretical predictions led to significant extensions of spectral analyses toward higher energy ranges. Theoretical line lists for ammonia (Huang et al 2011a,b;Yurchenko et al 2009) and phosphine (Yurchenko et al 2006;Sousa-Silva et al 2014;Nikitin et al 2014;Rey et al, in prep.…”

“…In case of triatomics, such as water isotopic species (Yurchenko et al 2009;Barber et al 2011), carbon dioxide (Huang et al 2013(Huang et al , 2014, and ozone accurate theoretical predictions led to significant extensions of spectral analyses toward higher energy ranges. Theoretical line lists for ammonia (Huang et al 2011a,b;Yurchenko et al 2009) and phosphine (Yurchenko et al 2006;Sousa-Silva et al 2014;Nikitin et al 2014;Rey et al, in prep. ) are successful examples of such a trend for fouratomics.…”

ExoMol line lists – VIII. A variationally computed line list for hot formaldehyde

“…The maximum polyad number Pmax restricts the number of combinations of φ (i) n i and Φ (i,j) n i ,n j for which P Pmax. The resulting eigenfunctions Ψ J =0,Γ i obtained for each C2v(M) symmetry Γ = A1, A2, B1 and B2 together with the symmetrized rigid rotor wavefunctions |J, K, τrot form our J = 0 basis set representation (Yurchenko et al 2009), where the ro-vibrational basis functions are given as a direct product of Ψ J =0,Γ i and |J, K, τrot . Here τrot is the rotational parity defined by Yurchenko et al (2005a), and K is the projection of the angular momentum on the body-fixed axis z.…”

Ground-state ammonia and water in absorption towards Sgr B2

“…The molecular data included not only the rotational and inversion transitions, but also vibrational transitions. The energies, transition frequencies, and transition probabilities were taken from the ab initio calculations of Yurchenko et al (2009). In the current model, 847 states and 7803 radiative transitions were considered.…”