Observing organic molecules in interstellar gases: Non equilibrium excitation. LAURENT WIESENFELD, ALEXANDRE FAURE, Grenoble, France ANTHONY REMIJAN, National Radio Astronomy Observatory, Charlottesville, VA KRZYSZTOF SZALEWICZ, University of Delaware, Newark, DE. ISMS Champaign June

Observing molecules: a question of collisions Interactions Molecule M, with dipole moment µ diluted in a gas of H 2 (H, He, e - ) Strong interactions with photons: Thermal bath of photon T photon = T internal (M) Strong interaction with H 2 T kinetic (H 2 ) = T internal (M) How ? ISMS Champaign June J2J2 l J1J1

Level populations Levels and Temperature; Equilibrium with the photon gas or the buffer gas Out of equilibrium : no T. Competition between photon interactions and collisions ALMA Workshop Copenhagen Energy J=0 J=1 J=2 J=3 T Population P = exp(-E/kT) no T Population Energy Super cooling

Level populations Levels and Temperature; Equilibrium with the photon gas or the buffer gas Out of equilibrium : no T. Competition between photon interactions and collisions ALMA Workshop Copenhagen Energy J=0 J=1 J=2 J=3 T Population P = exp(-E/kT) no T Population Energy Masing

How to compute the collision coefficients: ISMS Champaign June Potential energy surface (Force field, classically thinking) Dynamical calculation 1. Computing interaction of molecule and H 2 /He : ab initio quantum chemistry.  Potential at N points 2. Fitting N points onto one functional F (R, angles) 3. Performing quantum or classical scattering

An exemple: H 2 CO – H 2 PES computed at CCSD(T) – R12 level aug cc- pVTZ level. Show one van der Waals minimum. ISMS Champaign June

OBSERVATIONS ISMS Champaign June

Heavy molecules: a question of spectroscopy (1) Both H 2 CO and HCOOCH 3 are prolate asymmetric tops. But : HCOOCH 3 does not come into ortho-para / A and E forms nearly equivalent Observations: HCOOCH 3 weakly masing (superradiant) Brown et al ApJ 1975, Menten 2004, Churchwell et al ApJ ISMS Champaign June A. Faure, A.J. Remijan, K. Szalewicz and LW; ApJ, 2014.

Heavy molecules: a question of spectroscopy (2) Both H 2 CO and HCOOCH 3 are prolate asymmetric tops. But : H 2 CO comes into ortho and para forms Observations: H 2 CO supercooling Absorption against the cosmic microwave background  T internal ≈ 1.9 K (Townes & Cheung, ApJ 1976; Garrison et al., JCP 1976) ISMS Champaign June  1 11 absorption at GHz N. Troscompt et al, A&A LW, A Faure, MNRAS 2013 GBT observation of pre-stellar core B68.

METHYL FORMATE ISMS Champaign June

ISMS Champaign June HCOOCH 3 - He highly anisotropic potential A Faure, K Szalewicz, LW JCP, 2011 ; A Faure P. Remijan,K. Szalewicz, LW ApJ 2013

ISMS Champaign June A - HCOOCH 3

ISMS Champaign June A - HCOOCH 3

FORMALDEHYDE ISMS Champaign June

The opposite : H 2 CO Ortho and para forms are disconnected Overpopulation of the lowest level, 1 11 ISMS Champaign June PREFERENTIAL COLLISION TOWARDS lower level 1 11

The opposite : H 2 CO Ortho and para forms are disconnected Overpopulation of the lowest level, 1 11 ISMS Champaign June PREFERENTIAL COLLISION TOWARDS the lower level 1 11

Conclusion Non equilibrium excitation of low-lying levels (GBT/VLA, not ALMA frequencies !!) Need intimate knowledge of excitation/de-excitation schemes as well as opacity effects For high lying masers, same type of knowledge will be requested. Much tougher to compute Ex: H 2 O v> 0 excitation tremendously long to compute (>> week/energy point, 12 cores, up to date codes). High lying levels of COM's also at the limit of possibilities, in an exact fashion (same precision in any state-to-state collision) QCT difficult, because of subsequent quantization. We keep on trying ! ISMS Champaign June

Part of a large effort aiming at computing collision coefficients between light or heavy molecules with H 2, both ortho and para. ISMS Champaign June Who, where. L. WIESENFELD, A. FAURE, C. RIST, C. CECCARELLI, B. LEFLOCH, N. Troscompt, M. Wernli, F. Daniel Ongoing collaborations: Paris, Meudon, Le Havre, Dijon, Lille, Orsay, Rennes, Bordeaux (FR) Nijmegen (NL), JPL-Pasadena, Delaware, NRAO (US), Durham (UK), Madrid (SP), €, $ : EU FP6 ‘Molecular Universe’, CHESS KP HSO CNES, ANR FORCOMS - HYDRIDES COST programs ‘ The Chemical Cosmos’,'Our Astrochmical History'. PCMI-INSU-CNRS, LABEX NWO (NL), NASA-JPL