Competition between CO and N-2 desorption from interstellar ices

K.I. Öberg, F. van Broekhuizen, H.J. Fraser, S.E. Bisschop, E.F. van Dishoeck, S. Schlemmer

Research output: Contribution to journalArticle

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Abstract

Millimeter observations of pre- and protostellar cores show that the abundances of the gas-phase tracer molecules, C18O and N2H+, anticorrelate with each other and often exhibit 'holes' where the density is greatest. These results are reasonably reproduced by astrochemical models, provided that the ratio between the binding energies of N2 and CO, RBE, is taken to be between 0.5 and 0.75. This Letter is the first experimental report of the desorption of CO and N2 from layered and mixed ices at temperatures relevant to dense cores, studied under ultrahigh vacuum laboratory conditions using temperature programmed desorption. From control experiments with pure ices, RBE=0.923±0.003, given Eb(N2-N2)=790±25 K and Eb(CO-CO)=855±25 K. In mixed (CO:N2=1:1) and layered (CO above or below N2) ice systems, both molecules become mobile within the ice matrix at temperatures as low as 20 K and appear miscible. Consequently, although a fraction of the deposited N2 desorbs at lower temperatures than CO, up to 50% of the N2 molecules leave the surface as the CO itself desorbs, a process not included in existing gas-grain models. This codesorption suggests that for a fraction of the frozen-out molecules, RBE is unity. The relative difference between the CO and N2 binding energies as derived from these experiments is therefore significantly less than that currently adopted in astrochemical models.
LanguageEnglish
PagesL33-L36
JournalAstrophysical Journal
Volume621
Issue number1
DOIs
Publication statusPublished - Mar 2005

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desorption
ice
molecules
binding energy
temperature
gas
ultrahigh vacuum
tracers
energy
unity
experiment
tracer
vapor phases
matrix
matrices
gases

Keywords

  • astrochemistry
  • infrared
  • molecules
  • nanoscience

Cite this

Öberg, K. I., van Broekhuizen, F., Fraser, H. J., Bisschop, S. E., van Dishoeck, E. F., & Schlemmer, S. (2005). Competition between CO and N-2 desorption from interstellar ices. Astrophysical Journal, 621(1), L33-L36. https://doi.org/10.1086/428901
Öberg, K.I. ; van Broekhuizen, F. ; Fraser, H.J. ; Bisschop, S.E. ; van Dishoeck, E.F. ; Schlemmer, S. / Competition between CO and N-2 desorption from interstellar ices. In: Astrophysical Journal. 2005 ; Vol. 621, No. 1. pp. L33-L36.
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Öberg, KI, van Broekhuizen, F, Fraser, HJ, Bisschop, SE, van Dishoeck, EF & Schlemmer, S 2005, 'Competition between CO and N-2 desorption from interstellar ices' Astrophysical Journal, vol. 621, no. 1, pp. L33-L36. https://doi.org/10.1086/428901

Competition between CO and N-2 desorption from interstellar ices. / Öberg, K.I.; van Broekhuizen, F.; Fraser, H.J.; Bisschop, S.E.; van Dishoeck, E.F.; Schlemmer, S.

In: Astrophysical Journal, Vol. 621, No. 1, 03.2005, p. L33-L36.

Research output: Contribution to journalArticle

TY - JOUR

T1 - Competition between CO and N-2 desorption from interstellar ices

AU - Öberg, K.I.

AU - van Broekhuizen, F.

AU - Fraser, H.J.

AU - Bisschop, S.E.

AU - van Dishoeck, E.F.

AU - Schlemmer, S.

PY - 2005/3

Y1 - 2005/3

N2 - Millimeter observations of pre- and protostellar cores show that the abundances of the gas-phase tracer molecules, C18O and N2H+, anticorrelate with each other and often exhibit 'holes' where the density is greatest. These results are reasonably reproduced by astrochemical models, provided that the ratio between the binding energies of N2 and CO, RBE, is taken to be between 0.5 and 0.75. This Letter is the first experimental report of the desorption of CO and N2 from layered and mixed ices at temperatures relevant to dense cores, studied under ultrahigh vacuum laboratory conditions using temperature programmed desorption. From control experiments with pure ices, RBE=0.923±0.003, given Eb(N2-N2)=790±25 K and Eb(CO-CO)=855±25 K. In mixed (CO:N2=1:1) and layered (CO above or below N2) ice systems, both molecules become mobile within the ice matrix at temperatures as low as 20 K and appear miscible. Consequently, although a fraction of the deposited N2 desorbs at lower temperatures than CO, up to 50% of the N2 molecules leave the surface as the CO itself desorbs, a process not included in existing gas-grain models. This codesorption suggests that for a fraction of the frozen-out molecules, RBE is unity. The relative difference between the CO and N2 binding energies as derived from these experiments is therefore significantly less than that currently adopted in astrochemical models.

AB - Millimeter observations of pre- and protostellar cores show that the abundances of the gas-phase tracer molecules, C18O and N2H+, anticorrelate with each other and often exhibit 'holes' where the density is greatest. These results are reasonably reproduced by astrochemical models, provided that the ratio between the binding energies of N2 and CO, RBE, is taken to be between 0.5 and 0.75. This Letter is the first experimental report of the desorption of CO and N2 from layered and mixed ices at temperatures relevant to dense cores, studied under ultrahigh vacuum laboratory conditions using temperature programmed desorption. From control experiments with pure ices, RBE=0.923±0.003, given Eb(N2-N2)=790±25 K and Eb(CO-CO)=855±25 K. In mixed (CO:N2=1:1) and layered (CO above or below N2) ice systems, both molecules become mobile within the ice matrix at temperatures as low as 20 K and appear miscible. Consequently, although a fraction of the deposited N2 desorbs at lower temperatures than CO, up to 50% of the N2 molecules leave the surface as the CO itself desorbs, a process not included in existing gas-grain models. This codesorption suggests that for a fraction of the frozen-out molecules, RBE is unity. The relative difference between the CO and N2 binding energies as derived from these experiments is therefore significantly less than that currently adopted in astrochemical models.

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KW - infrared

KW - molecules

KW - nanoscience

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U2 - 10.1086/428901

DO - 10.1086/428901

M3 - Article

VL - 621

SP - L33-L36

JO - Astrophysical Journal

T2 - Astrophysical Journal

JF - Astrophysical Journal

SN - 0004-637X

IS - 1

ER -

Öberg KI, van Broekhuizen F, Fraser HJ, Bisschop SE, van Dishoeck EF, Schlemmer S. Competition between CO and N-2 desorption from interstellar ices. Astrophysical Journal. 2005 Mar;621(1):L33-L36. https://doi.org/10.1086/428901