Entropy Effects in the Fragmentation of 1,1-Dimethylhydrazine Ions
Bibliographic record
Abstract
The 1,1-dimethylhydrazine ion ((CH3)2NNH2+*) has two low-energy dissociation channels, the loss of a hydrogen atom to form the fragment ion m/z 59, (CH3)(CH2)NNH2+, and the loss of a methyl radical to form the fragment ion m/z 45, the methylhydrazyl cation, CH3NNH2+. The dissociation of the 1,1-dimethylhydrazine ion has been investigated using threshold photoelectron-photoion coincidence (TPEPICO) spectroscopy, in the photon energy range 8.25-31 eV, and tandem mass spectrometry. Theoretical breakdown curves have been obtained from a variational transition state theory (VTST) modeling of the two reaction channels and compared to those obtained from experiment. Seven transition states have been found at the B3-LYP/6-31+G(d) level of theory for the methyl radical loss channel in the internal energy range of 2.32-3.56 eV. The methyl loss channel transition states are found at R(N-C) = 4.265, 4.065, 3.965, 3.165, 2.765, 2.665, and 2.565 A over this internal energy range. Three transition states have been found for the hydrogen atom loss channel: R(H-C) = 2.298, 2.198, and 2.098 A. The DeltaS++(45) value, at an internal energy of 2.32 eV and a bond distance of R(N-C) = 4.265 A, is 65 J K-1 mol-1. As the internal energy increases to 3.56 eV the variational transition state moves to lower R value so that at R(N-C) = 2.565 A, the DeltaS++ decreases to 29 J K-1 mol-1. For the hydrogen atom loss channel the variation in DeltaS++ is less than that for the methyl loss channel. To obtain agreement with the experimental breakdown curves, DeltaS++(59) = 26-16 J K-1 mol-1 over the studied internal energy range. The 0 K enthalpies of formation (DeltafH0) for the two fragment ions m/z 45 and m/z 59 have been calculated from the 0 K activation energies (E0) obtained from the fitting procedure: DeltafH0[CH3NNH2+] = 906 +/- 6 kJ mol-1 and DeltafH0[(CH3)(CH2)NNH2+] = 822 +/- 7 kJ mol-1. The calculated G3 values are DeltafH0[CH3NNH2+] = 911 kJ mol-1 and DeltafH0[(CH3)(CH2)NNH2+] = 825 kJ mol-1. In addition to the two low-energy dissociation products, 21 other fragment ions have been observed in the dissociation of the 1,1-dimethylhydrazine ion as the photon energy was increased. Their appearance energies are reported.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.000 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.000 | 0.001 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".