Subject: Singlet-Triplet Summary!

From: [email-masked] (Magda Wajrak)
Date: Tue, 13 Jun 95 17:24:01 WST

Dear Netters,

I had few people asking me for a summary on my question regarding
the singlet-triplet splitting. I posted two questions regarding
singlet-triplet splitting, below are the questions and answers
I received:

Q1.
> I would like to ask for some help in locating some articles or books
> which give singlet-triplet energy splittings of some
> simple sulfur and/or nitrogen containing compounds. I
> especially need experimental results, but theoretical
> results would also be helpfull.

ANSWERS:

I've been using semi-empirical methods to calculate singlet triplet gaps 
of aryl nitrenium ions.  Here are some related references.

Cramer and Dulles, JACS, 1994, 116, 9787
Gibson, Greene, and Berkowitz, JCP, 1985, 83, 4319
Ford and Scribner, JACS, 1981, 103, 4281
Glover and Scott, Tetrahedron, 1989, 45, 1763
Falvey and Cramer, Tetrahedron Lett., 1992, 33, 1705
Li, Abramovitch and Houk, JOC, 1989, 54, 2911

If you can read the world wide web Dulles and Cramer have a poster:

http://hackberry.chem.niu.edu:70/0/ECCC/homepage.html Poster 59

Hope this was a help.

Rick Edgington

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   My group has been interested in S-T gaps in nitrenium ions for some time.
Our recent efforts have focused on DFT, which is very successful in this
regard. You might be interested in the following articles:

        Falvey, D. E.; Cramer, C. J. "Aryl- and Alkylnitrenium Ions:
Singlet-Triplet Gaps via Ab Initio and Semi-Empirical Methods" Tetrahedron
Lett. 1992, 33, 1705.

34.     Cramer, C. J.; Dulles, F. J.; Storer, J. W.; Worthington, S. E. "Full
Valence Complete Active Space SCF, Multireference CI, and Density Functional
Calculations of 1A1-3B1 Singlet-Triplet Gaps for the Valence-Isoelectronic
Series BH2-, CH2, NH2+, AlH2-, SiH2, PH2+, GaH2-, GeH2, and
AsH2+" Chem. Phys. Lett. 1994, 218, 387.

40.     Cramer, C. J.; Dulles, F. J.; Falvey, D. E. "Ab Initio
Characterization of Phenylnitrenium and Phenylcarbene:  Remarkably Different
Properties for Isoelectronic Species" J. Am. Chem. Soc. 1994, 116, 9787.

45.     Worthington, S. E.; Cramer, C. J.; Dulles, F. J. "The Electronic
Structures of Aziridenium and Cyclopropylidene. Hypovalent Atoms in
Three-Membered Rings" J. Phys. Chem. 1995, 99, 1462.

55.     Lim, M. H.; Worthington, S. E.; Dulles, F. J.; Cramer, C. J. "Density
Functional Calculations of Radicals and Diradicals" in Density-Functional
Methods in Chemistry, ACS Symposium Series ###, Laird, B. B.; Ziegler, T.;
Ross, R., Eds.; American Chemical Society:  Washington, DC, submitted for
publication.

   The TL paper is simply qualitative about what factors influence the gap,
the remaining four are more quantitative in nature. Although all are
theoretical, they contain many references to experimental work. (For the
submitted book chapter, I would be happy to send you a preprint if you are
interested. It covers methyl- and dimethylnitrenium, as well as the triplet
and first excited state singlets of diazene).

Chris

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Q2
> What is the singlet-triplet experimental gap data for Sulfur atom
> and S2 molecule?

ANSWERS:

1) Atomic species.  The standard source of data for atoms is C. E. Moore,
"Atomic Energy Levels", Vol. I,II,III, US National Bureau of Standards,
Circular No. 467, US Government Printing Office, 1958. 

2) Molecular species. Refer to the compendium of spectroscopic data on diatomic
species by Gehard Herzberg. K. P. Huber and G. Herzberg, "Constants of Diatomic
Molecules", van Nostrand-Reinhold (1979).  Sometimes the required data can be
found in the JANAF Thermochemical Tables. Herzberg only discusses states of the
triplet S2 species in his mongraph "Spectra of Diatomic Molecules".

In the case of atomic sulfur, the excited singlet D state is 9238.58
wavenumbers (1/cm) above the triplet P (j=0) state.  There are no data on the
singlet-triplet energy difference for S2 in the edition of JANAF in my office.

I hope this helps.

Wayne Steinmetz
Carnegie Professor

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   My supervisor forwarded a message from you. We have published a couple
  of theoretical papers, which have included work on the singlet/triplet
  splittings of S2 and S. The experimental results we quoted were from the
  JANAF Thermochemical Tables, and put the splittings at (in kcal/mol):
  S (26.4), S2 (13.4). We had difficulties reproducing the experimental
  results using all sorts of levels of theory with QCISD(T) data leading
  to values of: S (33.4) and S2 (18.0). See our paper (J. Chem. Phys.
  98, 5566 (1993) or another J. Chem. Phys. 96, 7449 (1992)).
  Rob.

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Magdalena Wajrak