James (Jim) K G Watson
Jim identified CH as the carrier of an unusually narrow DIB, much narrower than the standard DIBs.
The Watsonian
Among the papers I have been forced to understand, there is hardly one I found so difficult as Watson’s milestone study in which he simplified the vibration–rotation Hamiltonian for polyatomic molecules, originally derived by Wilson and Howard.
Miljenko Perić
In his paper, Miljenko Perić writes "Just to reproduce five pages of this paper, I needed a whole month, and in order to decipher the extremely complicated formulae in condensed Levi-Civita form, I penned several hundreds of leaves. It seems that other people also had similar problems.
"I found once in a very serious paper the sentence: “If the Watson’s Hamiltonian is correct …”. Even Watson himself wrote in his paper, “The simplicity of the final result suggests that it should be obtainable by a less complicated calculation than that described here, I have, however, been unable to find a more direct derivation.”
"As another illustration of the complexity of this study, Watson needed two years to apply the same procedure for deriving the Hamiltonian for linear polyatomic molecules. Some researchers questioned his results, and Watson’s answer to this criticism came only seven years later.
"Thus, the goal of the present study was to attempt to derive Watson’s Hamiltonian in a less elegant but simpler, or at least more straightforward, way."
Maybe Miljenko should have had a shot of single malt whisky to see the Jim Watson Levi Civita way!
Download Miljenko Perić's paper (PDF, 611KB)
Arguably the first DIB identified
Far Ultraviolet lines of interstellar CH, including one DIB, James K G Watson
Steacie Institute for Molecular Sciences, National Research Council of Canada, Ottawa, Ontario, Canada K1A 0R6.
A far-ultraviolet flash-photolysis spectrum of CH was published in 1969 by Herzberg and Johns (a), but no rotational assignments were made.
From their list of 45 lines in the 3d X2 band, there are three near-coincidences with unidentified (UID) interstellar lines (b) at 1368.74, 1369.13, and 1370.87 A towards the star Ophiuchi.
The spectra of other electronic transitions of CH towards this star are well known, and it was decided to use the interstellar lines as giving the positions of lines with J 00 = 0:5, as is found for the other interstellar bands. From this, a rotational analysis of the complete band was possible, using a Rydberg-state program previously used for the ArH and ArD molecules. (c)
An interesting aspect of this assignment is that the 1369.13 A line is classified (d) as the only established ultraviolet ‘diffuse interstellar line’ (DIB). Different broadening of different lines is also seen in the laboratory spectrum, and is attributed to pre-dissociation, which is found to be greater for lines with upper levels of d parity, including the DIB, than for lines with upper levels of c parity, consistent with the dominant pre-dissociating state being a 2 state.
From the n3 -dependence of the splittings of the nd complexes, the rotational structure of the 4d X2 band is predicted, and allows the assignment of the UID interstellar line at 1270.96 A˚ (e) to the strongest J 00 = 0:5 line of this band.
(a) G. Herzberg and J. W. C. Johns, Ap. J. 158, 399 (1969).
(b) J. A. Cardelli, B. D. Savage, and D. C. Ebbets, Ap. J. 383, L23 (1991).
(c) I. Dabrowski, D. W. Tokaryk, M. Vervloet, and J. K. G. Watson, J. Chem. Phys. 104, 8245 (1996).
(d) T. M. Tripp, J. A. Cardelli, B. D. Savage, Ap. J. 107, 645 (1994).
(e) S. R. Federman, J. A. Cardelli, E. F. van Dishoeck, D. L. Lambert, and J. H. Black, Ap. J. 445, 325 (1995).
Articles and papers
- 'An introduction to the spectroscopy of H3+' James Watson, The Royal Society, 15 September 2000.
- 'The Molecular Hamiltonian' Henning Meyer, Annual Reviews, October 2002.