You can use the formula E*lambda = h * c and solve for lambda. I just put this here into the google search:

c*h/(410 kJ / 6,02e23)

and it gives me 291.6 nm. Should be correct.

I do not think that it is as simple as Mr Hoffmann's suggestion. Even ı do not have the full answer, at least the Work function should be added to equation (as far as i remember).

I am pretty sure that I am right. What should the work function have to do with single bond breaking? Also, the bond dissociation energy is defined pretty well as the energy that is needed to break the bond, no extra energy needed. So the energy just needs to be calculated for a single bond by dividing the number by the avogadro number and then you need to calculate the wavelength of a photon with that specific energy.

Take a look into the Wikipedia article that also chooses the C-H bond as an example. http://en.wikipedia.org/wiki/Bond-dissociation_energy

Dear Dr. Hoffmann, 

We may have understood the question in different perspective. My answer is more concerned with the localization of the electron with respect to atoms that it was bonded . Because, if the electron's location is not valid there is a high chance of rearrangement while we are talking about organic molecules. So, my perspective's concern is the after cleavage situation and remaining type of species to help with the final aim of the first question. Please do not be offended which is a situation that was never my intent. By the way, Thank you very much for your informative comment. 

I agree with Dr. Björn Hoffmann . BDE values are listed in many references & they are average values. Take the BDE of the bond, you are interested in, & apply the relation: wavelength= h.c/E (where h is Planck's constant; c= speed of light; and E is BDE). Take care of the units to calculate the wavelength in nanometers.

The only problem is that hydrocarbons do NOT dissociate at this wavelength (about 300 nm). Saturated hydrocarbons even do not absorb at this wavelength (see e.g. http://www.uobabylon.edu.iq/eprints/publication_11_8282_250.pdf). Formally the equation is OK, but bods cannot be dissociated individually.. Light interacts with delocalized molecular orbitals. Sigma bonds absorb around 150 nm (far vacuum UV). The molecular orbital energies can estimated experimentally using photoelectron spectroscopy (see e.g. http://pubs.acs.org/doi/abs/10.1021/ja00102a041). Localized bond energies come for the chemical view of molecules and are calculated from heats of formation using certain models, but cannot be measured directly. In quantum chemical calculations there are so-called "localization" techniques which transform the delocalized molecular orbitals into localized, bond-specific ones but these are not eigenfunctions of any operator, therefore are not related to measurable quantities.

:)

I agree with Dr Hoffman, the photon energy must be sufficient to initiate dissociation of the bond. The energy of the photon is govern by E=hv.

Thank you all for your valuable answers and comments. I hope a lot can be discussed further on bond dissociation energy, bond order, etc.

Regards,

OSK

Can we calculate the BDE by non-destructive method ?

Gyorgy Banhegyi Björn Hoffmann Stewart Wilson Nizar Matar Kerem Karakuş Björn Hoffmann

Thank you for your valuable insights and remarks on how to calculate the wavelength required for bond dissociation in a molecule.

I guess, we can also find it by using the formula we use to find out the vibrational frequency ?

Stewart Wilson Gyorgy Banhegyi Nizar Matar Kerem Karakuş Björn Hoffmann

What are the non-destructive means of finding bond energies of molecules ?

Hello Omkar, It is possible to perform quantum chemical calculations, but these will not yield directly bond energy. Bond energy as such cannot be observed experimentally, only the disruption of the molecule. Bond energy is a useful concept, but not too exact. If you look at the history of the concept, you will see that it started from thermochemistry (oxidation energy calculations) using certain assumptions. Later the Hückel theory for pi-systems allowed the calculation of sigma+pi bond orders that were correlated with bond lenghts (successfully). Later, as quantum chemistry advanced, it was possible to calculate total energies and molecular orbital energies (the letter can be approximately determined by UV or X-ray photoelectron spectroscopy). But these observable characteristics are inherently delolcalized. Later quantum chemical methods based on localized orbitals were also introduced, which are intuitive but cannot be osberved or measured. So either you perform detructive methods and measure experimentally the dissociation energies of the molecules and attribute (arbitrarily) energies to the separate bonds or you calculate the total energies of the fragments and do the same thing using calculated or experimenttal data. Nowadays rather calculated bond orders are used to characterize the individual bonds. Nevertheless the bodn energy is a useful (approximate) and intuitive concept that can be well used in education.

Dear RG Members,

Please follow the updates about the Nobel Prizes on this link:

https://www.researchgate.net/project/The-Nobel-Prize-2

Don't forget to give your feedback/recommendations. Excuse me for repeated request.

Regards, OSK