NH2OH Paper Notes, progress, emails, relevant papers and other correspondence:

• Discussion Topics:
  • NH2OH - absence in these sources:
  • Bulleted Points:
    • (From Garrod et al) --NH2OH is formed on grains from the addition reaction NH + OH -- followed by hydrogenation (really?). As OH becomes more mobile , the addition reaction OH + NH2 --> becomes dominant.
    • Garrod et al. -- column density on the order of 4x10^(-7) - 4 x 10^(-6)
    • The question Tony asked is does NO hydrogenate as CO does? This is suggested by Charnley et al. However, no further investigation is made. * We know that NO is depleted toward the density peaks of the protostellar cores L1544 and L183 -- what are the formation mechanisms for NO? What about nitrogen chemistry in general.
      • Going to quote the NO abundance reported for different sources
    • Major point of the discussion from this.... Garrod et al. claims that on grains, NH2OH is formed from the reaction of NH + OH, follow by hydrogenation. However, does NO hydrogenate as CO does? Charnley has a brief statement about this, but there are ZERO studies currently suggesting that NO goes through the hydrogenation process much like CO. And given the different states of these molecuels (CO being a singlet sigma and NO being a doublet Pi (double check that)), it doesn't seem likely that NO would just follow through with this same process... so I would lightly conclude at this point that no, NO does not hydrogenate like CO. This could account for why the Garrod et al. model predicts higher abundances while NH2OH isn't present (at least at the limits of the survey data).
    • The NO hydrogenation if it occurs (what are teh energies for these? Or possible reactions for some of these ... ie what is the formation mechanism for HNO? or NOH? and the energy involved)
      • NO + H --> NOH + H --> NHOH + H --> NH2OH ???
      • NO + H --> HNO + H --> H2NO + H --> NH2OH ???
      • or who is to say this doesn't happen -- NO + H --> NHO + H --> H2N + H --> H3NO+ ??? (not likely)
    • It should noted that an experimental study of a solid argon matrix, the NH2 disappears when the ice sample is warmed up to 20K. This is because NH2 recombines with H very efficiently. This is only the case fo NH3 in an inert matrix. In ices, NH3 or H2O with other simple molecules, the active hydrogen generated by UV excitation collides with a molecules in the ice. Also, a free hydrogen atom may abstract hydrogen yielding a H2 molecule. This therefore, would leave the NH2 radical free to possibility combine with other radical species (such as OH). But how efficiently would it combine with a species that is less abundance than H on the ice (ie would the free hydrogen neutralize NH2 before it could combine with OH??)
    • Is there perhaps a temperature problem here?
      • Temperature method versus types of ices:
        • Kaiser suggests that the temperture of at least 174 K was required before NH2OH was observed.
        • Garrod et al.-- The temperature ranges with the reported abundances of 114K-122K.
      • The difference between these two methods. 1) Kaiser et al. assumes NH3 + H2O ices. This comes off in the gass phase at higher temperatures. 2) Garrod et al. assumes ices with organic species. These types of ices evaporate at much lower temperatures.
        • I am still looking into this. I have never studied ices and I am a little swamped with the large amoutn of information on this topic. Namely I am just looking for work that describes (or theoretically claims) what type of ice mantles form in these different environments and what temperature are teh various ices known to begin the sublimation process? Is this even know?
        • Essentially I am missing information that I would like to put in the discussion section here.
      • If we go with Keisers NH3 + H2O ice model, then one possible explanation of not detecting NH2OH in these sources would be that temperatures are not warm enough for NH2OH to be found in the gas phase. However, I assume that the ices in these sources are not just NH3 + H2O. So, what are the expected ices to be found in hot cores vs. dense cloud regions. Is the Garrod et al. model using the correct ice assumptions? I assume they would have this correct to what is at least expected?
      • Some answers: (From Kaiser et al.) Ammonia might also exist on dust grains in cold molecular clouds with an abundance between 1-10% with respect to H2O.
      • Kaiser et al. summary:
        • Suggests that NH2OH is formed from the recombination of NH2 + OH radicals inside of ices.
        • Their experiment: Used a 10% ammonia to water gas mixture for the ices. This was condensed at 10 K and then heated up to 130 K and recrystallized at 10 or 50 K (to achieve a crystalline phase). Samples were then irradiated with radiation equivalent to that found in the Kuiper belt over 108 years. Samples were then heated at a rate of 0.5K/min and monitored using both mass spectrometer and using infrared spectroscopy. Species detected using MS and IR are H2, N2, O2/N2H4, NH2OH, H2O2. Hydroxlyamine (NH2OH) was not detected until it was released from the ices between 160-180K.
    • What about protonated hydroxlyamine? does NH2OH quickly protonate to NH3OH+ or NH2+OH2+:
      • Largo et al.: Studied the stability of ionized hydroxlyamine in teh ISM. Conclusion: the analysis of the potential energy surfaces corresponding to the reactison of molecular H2 with both protonated and ionized hydroxlyamine cannot proceed under interstellar conditions. They believe because of this, both of these species are then available to participate in sythetic routes to amino acid production. (NH3OH+ is the most stable isomer.) So, if NH3OH+ and NH2OH2+ are formed within interstellar conditions, then it is stable enough to hang around for longer periods than NH2OH. The biggest problem with this is that we cannot search for NH3OH+ because the rotational spectrum is not characterized (side note: I want to try this in the Pate lab... Brent has informed me that they will have the 40-60 GHz setup going and trying protonated methanol. So I am going to see if they can just throw in a sample of NH3 and H2O or H2O2 with a discharge.).
      • Blagojevic et al: NH2OH has a very high proton affinity (~194 kcal mol -1) and it therefore can be easily protonated in the gas phase of the interstellar medium through possible proton donors including H3+, HCO+, CH5+, H3O+. So, is it possible that even if NH2OH is forming that is nearly immediately undergoes protonation?
      • Snow et al.: According to B3LYP calcuations, a proton migrates from CH5+ to the NH2 group of NH2OH without a barrier, forming NH3OH+. The reactions is very exothermic (62.6 kcal/mol) and thus can allow for a shift to a higher energy isomer NH2OH2+. The reaction barrier to the shift is lower than the dissociation limit to NH2OH, thus this reaction can occur, forming both NH3OH+ and NH2OH2+.
      • Boulet et al.: Calculations show that the reaction of NH2OH + H3+ is also exothermically favorable. the produce of NH3OH+ being the more favorable product. The reaction does not require an activation energy. However, the author comments that the presence of these protonated species might be low in abundance due to dissociative recombination.
        • NH3OH+ + e- --> NH3 + OH
        • NH2OH2+ + e- --> NH2 + H2O
        • these are very exothermic reactions and favorable. and basically returns the species back to the originial interstellar radicals.
      • So, it could be that NH2OH is formed as suggested by the Garrod et al. model. However, upon formation, the molecule is quickly protonated. The protonated species may be quickly dissociated.
        • A direct statement from Boulet et al: "No matter how NH2OH is synthesized, the present study suggests that the sequence of protonation + dissociative recombination reactions could result in very low abundance."
    • And then what about nitrogen chemistry in general:
      • This is where formamide and NH2CN comes into play. (Side note: We the J=1-0 and J=2-1 (all three) a-type transitions of these species with GBT data. I will get you the figures shortly. They are sitting on a jump drive that I misplaced. If I cannot find it this weekend, I will reproduce the images as i have the ascii files backed up on my desktop. This is also the section I am having the hardest time pulling together... I feel comfortable with the discussion topics to this point... and below are my notes on nitrogen chemistry).
      • Nitrogen is the fifth most abundant element in the Universe. It is thought to exist mostly as N2. However, N2 is not observable rotationally or vibrationally (no permanent dipole). Note: In comets, N2 abundance is very low and element nitrogen is low wrt the solar value (Cochran et al. 2000).
      • In a study by Maret et al, found that only a small fraction of nitrogen is in the gas phase of dense clouds and most of that is atomic.
      • What about NH3 as it is key to our reaction? Several formation routes to NH3, though not fully known. Suggested that NH3 was formed through:
        • H3+ + N --> NH2+ + H
        • NH4+ + e --> NH3 + H
      • However, this was never proven. Results in 1997 showed you get:
        • H3+ + N --> NH2+ + H
        • NH2+ _ H2 --> NH3+ + H (NH3+ rapidly moves to the next reaction)
        • NH3+ + H2 --> NH4+ + H (this is a fast reaction)
        • H2O+ + N --> NOH+ + H --> NO+ + H2
        • O2 + + N --> NO+ + O
      • Nitrogen chemistry is radically different than that of oxygen chemistry as expected in the gas phase of the ISM.
      • Oxygen chemistry proceeds at much higher reaction rates than nitrogen (From Snow and Bierbaum)
      • Oxygen chemistry versus nitrogen chemistry in the ISM?
      • N2 has been detected in diffuse clouds through the FUSE mission. The results put the abundance of N2 at higher ratio than expected by models. It is generally expected that in difusse clouds, gas phase hemistry is the dominating factor and that grain chemistry doesn't play a huge role (except in H2). And for dense clouds grain chemistry is expected to pay a bigger role. These observations could suggest that perhaps grain chemistry play a bigger role than expected.
      • Now... what I am missing is the connection between the chemistry of these sources and possible connections with the formamide and NH2CN.

• Email from Robin - 10/05/2010:
  • So here is the most compelling scan I found for NH2OH. In the figure, the offsets I have marked of -93, -152, and -217 correspond to the respective transitions of J(Ka,Kc) = 2(1,1)-1(1,0), 2(0,2)-1(0,1), and 2(1,2)-1(1,1). These should be the strongest transitions within the 3mm region, and the strongest of all should be 2(0,2)-1(0,1) (@ offset -152) and as you can see, only noise is present. So even though the 2(1,2)-1(1,1) transition is blended, I think it is safe to say that NH2OH is not in SGRB2N (or at least not abundant enough for us to be detecting it within the noise of this data). FILE LINKED HERE: NH2OH_100.pdf:

• Email from Brett - 09/27/2010:
  • The very first thing that struck me was considering if NO would hydrogenate like CO. From a chemistry standpoint these are very different molecules - they have different electronic configurations, different binding energies, and should certainly have different reactivities. Dave Woon published a paper in 2001 in ApJ (v 569, p 541) looking at the successive hydrogenation of CO to form CH3OH among other products. CH3OH is isoelectronic to NH2OH, so looking at its formation pathways and comparing to a similar route with NO could be instructive. A brief literature search has shown that in gas phase reactions on Earth, the addition of H to HCO to form formaldehyde is a barrier-free, very exothermic process that dominates hydrogen abstraction from HCO to form H2 and CO.
  • On the other hand, formation of H2NO or HNOH from HNO in similar reactions proceed through barriers of 2.7 and 9.0 kcal/mol, respectively, while hydrogen abstraction by H to form H2 and NO has a barrier of only 0.5 kcal/mol and abstraction by OH to form H2O + NO is barrier-free. Further, the formation of HNO in the first place can proceed through three reaction pathways, two of which have barriers themselves, decreasing the overall rate. I can provide references for any of these if they'd be useful.
  • All of this evidence leads me to believe, from at least a qualitative standpoint, that NO really shouldn't be reacting (at least via successive hydrogenation) like CO, as the thermodynamics (and most likely the kinetics) once either reach the HXO step are very different. If H2NO or HNOH are able to be formed readily by other reactions, my gut instinct is to say that hydrogenation of these species to H2NOH should be exothermic and fast, but I don't have any evidence yet to support this.
  • Now what I haven't had time to look into is how all of this would play out on a grain surface where the reaction barriers and rates are probably not the dominate factor in the reactions. I've gotten the code used by Susanna and co-workers in the GWWH paper you mention and will take a closer look at it to see just what they did and if they took these factors into account.

• Summary from Remijan - 09/21/2010:
  • One of the things to consider is if NO is on grain surfaces in the first place. If it isn't there was no way for it to hydrogenate to NH2OH like CO does.
  • According to SLWW, their reaction is: "NH2OH is formed initially by NH+OH addition on grains, followed by hydrogenation; however, as OH also becomes mobile, the addition reaction OH+NH2 -> NH2OH becomes dominant." SLWW predict a column density on the order of NH2CHO or CH3NH2.
  • I believe that NO (if on a grain) would hydrogenate to NH2OH and this is backed up by Charnley et al. 2001, A&A, 378, 1024 (attached paper). So the Akyilmaz, et al. 2007 paper (also attached) describes the freezing out of NO...they say "...NO, unlike NH3 and N2H+, is depleted toward the density peaks of the protostellar cores L1544 and L183." But the abundance is 4 orders of magnitude lower than CO...which would put the abundance way down!
  • For the intro of the paper, we have pieces of evidence that tell us NH2OH should be booming in star forming regions.
  • The data tell us otherwise. The question is why?
    • radical reaction scheme proposed by SLWW is wrong...NH or OH would hydrogenate to NH3 or H2O before they would ever find each other. We can calculate the hopping times of H at different temps and show this to be the case.
    • NO does not hydrogenate like CO...I dont have any proof of that and something we need to find out...
  • So, look at the attached papers as the piece of evidence we need to test the hypothesis that NH2OH should be an abundant molecule in SFRs from the context the NO is on grain surfaces. What we have to come up with is why we don't see it.

NH2OH - Relevant papers:

• aa6131-06.pdf: Akyilmaz, et al. 2007 paper
• aah2955.pdf: Charnley et al. 2001 paper
• NH2OH.pdf: NH2OH Initial Data summary from Remijan
• nh2oh.cat: NH2OH frequencies from JPL

• Persons/group who can change the list:
  • Set ALLOWTOPICCHANGE = AstrochemGroup

• 13936_0_art_file_467101_lxpnrx.pdf: 13936_0_art_file_467101_lxpnrx.pdf