Questions tagged [spectroscopy]

Use this tag for questions about spectroscopic methods in practice and in theory, especially where more specific tags for the individual method (such as [nmr-spectroscopy] or [ir-spectroscopy]) are not available.

Filter by
Sorted by
Tagged with
5
votes
1answer
94 views

Open resource for spectroscopic raw data

Is anyone aware of reliable resources (ideally public) which allow the user to download the raw spectroscopic data such as infrared spectrum of small organic molecules, or rotational spectrum of HCl/...
0
votes
1answer
48 views

laser diode problem [closed]

I'm a student studying chemistry, i'm working with diode laser to look at emission spectra for certain complexes. i'm using integrating sphere as my setup, when i use the 405nm diode laser output of 4....
1
vote
0answers
26 views

What is the best way to go about matching proton-NMR spectra to molecules?

I've attatched an example question. I have already solved this one, I'm wondering about what, in your experience, is the most time-efficient way of approaching a question like this one. I can solve ...
0
votes
0answers
44 views

Term symbols for excited nitrogen (2s2p^4 configuration)

Looking at the NIST levels listing for neutral nitrogen atom, one of the excited configuration is $2s2p^4$ configuration. https://physics.nist.gov/cgi-bin/ASD/energy1.pl?encodedlist=XXT2&de=0&...
0
votes
0answers
18 views

Why can't I make hexyl acetate from isoamyl acetate

In the organic chemistry course, we did a lab where we had to transform isoamyl acetate (banana) into hexyl acetate (pear). The experiment did not work. Indeed, we did a fractional distillation to ...
0
votes
0answers
26 views

Why are there only 2 peaks in proton NMR of 2-iodopropane? [closed]

I was reading about proton NMR and was drawing high resolution spectra for some of the molecules. I have currently drawn proton NMR spectra for ethanol and ethyl benzoate and got number of peaks as ...
2
votes
1answer
41 views

Do the spectra of compound materials combine linearly with respect to the ratios of the constituent compound spectra?

My question stems from reading this article on the FTIR spectrum of oil that has been mixed with various contaminants. If one has the spectrum for the original uncontaminated oil and the spectrum for ...
5
votes
2answers
337 views

Can all NMR spectrometers perform special techniques such as COSY, NOESY, HETCOR,..? [closed]

Do you need special spectrometers for: probing nuclei other than hydrogen or carbon? performing 2D spectroscopy such as COSY, NOESY, HETCOR, HSQC,.. Or are these techniques usually available on ...
1
vote
0answers
42 views

Effect of ionization on dipole moment

Suppose we have a non-dipolar molecule such as carbon dioxide. If carbon dioxide is ionized by some means in the gas-phase, will it develop a dipole moment? I am asking with reference to microwave ...
0
votes
1answer
42 views

Why do certain signals in proton NMR experience extensive splitting despite only having 1 neighbour?

I came across the compound 3-methylpentan-2-ol. Looking at its proton NMR spectra, it seems there is a lot of splitting for the signal at 4 ppm. I'm assuming that the 4 ppm represents the proton in ...
3
votes
1answer
29 views

Haemoglobin literature spectra does not match

I am studying haemoglobin absorption spectra in its oxygenated and deoxygenated state and I compiled values from different sources including: A PhD thesis by van Assendelft [1], using extinction ...
0
votes
1answer
38 views

How to perform IR spectroscopy of silica particles when they are flowing through pipe at different RH? [closed]

Silica particles surface bonds are susceptible to humidity and normally changes between silanol and siloxane with changing RH. I want to measure these properties of particles when they are in motion,i....
4
votes
1answer
54 views

What exchange timescales are needed to cause decoupling in NMR?

I'll try to explain the source of my confusion as clear as possible: (*) The methyl protons in toluene are decoupled because the C-C bond between the methyl group and benzene allows very fast ...
0
votes
0answers
22 views

why is the H-NMR chemical shift of methane lower than that for ethane?

If we replace one hydrogen in methane by a methyl group we arrive at ethane. Now we can say: Carbon is more electronegative, and so it withdraws electrons which leads to deshielding. This is why the ...
0
votes
0answers
26 views

Why does peak decoupling occur in H-NMR spectra?

For example, when we analyze the conversion of some chemical compound, certain characteristic areas tend to decrease (ok). However, why can a peak (i.e., one peak) generate smaller peaks (i.e., more ...
2
votes
1answer
51 views

Different force constant in ground vs excited state in spectroscopy

The force constant of iodine in the first excited state is $k=41.78$ N/m, and in the ground state it is $170$ N/m. I know that the formula for calculating $k$ is: $$ k= (\frac{ΔE_{vib} *2π}{h})^2 µ$$...
3
votes
0answers
46 views

Enantiomers to diasteroisomers (rotational spectra)

Enantiomers have identical rotational spectrum because their mass distributions are identical. Recently a trick has been introduced in microwave spectroscopy in which a enatiomerically pure gas chiral ...
7
votes
2answers
361 views

What is the difference between quantities reported as optical rotation and circular birefringence?

Optical activity gets complicated quickly and the following question is intended to avoid threshold confusion. The linked lecture note* seems very accessible to me and Table 10.6 in particular is ...
6
votes
1answer
119 views

Question about a line from Rosenfeld's paper on optical rotation

There are a lot of papers on optical rotation which cite Rosenfeld's (German) 1928 paper "Quantum mechanical theory of natural optical rotation..." [Quantenmechanische Theorie der naturlichen ...
6
votes
1answer
85 views

Beer's law: UV-Vis absorbance values exceeding 2

In classical analytical chemistry, absorbance values in Beer's law can theoretically range from 0 to infinity. As general rule of thumb neither high, nor very low absorbance are used for ...
3
votes
0answers
42 views

Why does Larmor precession occur in NMR?

Larmor precession is the phenomenon that in NMR the spin (and by default also the magnetic dipole moment) of protons does not line up with the applied magnetic field but rather precesses around this ...
2
votes
1answer
172 views

How can every atom have unique spectral lines?

Why does every element have unique spectral lines? I have studied that spectral lines help us to identify the properties of an element. This is because after excitation when the excited electron(s) ...
4
votes
1answer
85 views

How to find the lifetime of sodium atoms in the 3p using information on the spectral line width?

I am trying to find the lifetime of sodium atoms at the 3p state using the relationship between the spectral linewidth and the uncertainty principle: $$ \Delta E \times \Delta t = h / 4\pi $$ The ...
4
votes
0answers
45 views

Is there an anisotropy factor (g factor) for TDDFT Abs and CD calculations?

Experimentally, anisotropy factor is calculated by dividing the CD spectra by the absorbance spectra multiplying by a factor of 32980 (in order to get a nondimensional quantity) Theoretical ...
1
vote
0answers
15 views

LIF spectrum with laser-coupled levels lines as the strongest

Why, if I excited the OH molecule Q-branch transition, my LIF spectrum (recorded during and after the laser pulse) does not result in only Q line being the most prominent, but also P and R lines with $...
0
votes
1answer
62 views

Emission spectra (Be and Mg)

The line says Alkaline metals and their salts impart characteristic colour to an oxidising flame. This is because the heat from the flame excites the outermost orbital electron to higher energy ...
0
votes
0answers
34 views

Interpretation of Carbon-13 NMR Spectra for Chemically Similar Carbon Atoms

I am analyzing the Carbon-13 NMR data from a reaction I will be modifying. There is not NMR data available for the specific compound I am attempting to synthesize; however, the compound I am ...
1
vote
0answers
17 views

In UV photoelectron spectroscopy why are filled orbitals seen at a higher binding energy?

I understand that the partially filled Ni intersects the Fermi level as there is a change from filled to unfilled orbitals. But what is the explanation for the lower binding energy of the filled 3d Cu ...
2
votes
2answers
128 views

How can the formula of WD-40 remain a trade secret?

Wikipedia says WD-40's formula is a trade secret How can it remain a secret today? Can't mass spectrometers, NMR and other equipment be used to determine the structure of the compounds that go ...
1
vote
0answers
16 views

Difference in transition lifetimes for near-resonant v/s non-resonant Raman effect

I have read that a virtual state is created when Raman scattering occurs. Since this state is forbidden, the molecule upon absorbing a photon (not enough to take it to the next electronically excited ...
-2
votes
1answer
44 views

Difference between equations for spectroscopy wavenumbers

What is the difference between these two equations and when is appropriate to use which one? We were told that $F(J)$ in this case is $F(J)= E/h$ for units in frequency And $F(J) = BJ(J+1)$ $\...
0
votes
0answers
27 views

Rotational spectroscopy application of different equations [duplicate]

So we were given two problems and I don't understand why one was solved one way, and another was solved another way Estimate the bond length of 12C16O (pure rotational spectrum) given J''=3 (15.356 ...
1
vote
1answer
43 views

Determine bond length via rotational spectroscopy

Estimate the bond length of 12C16O (pure rotational spectrum) given J''=3 (15.356 cm-1) and J'=9 (38.356) I understand that the first step is the calculate the rotational constant. So to do this I ...
9
votes
1answer
121 views

Hybrid orbitals, photoionization and time dependence

Wikipedia, in the article on Orbital Hybridisation, states the following: One misconception concerning orbital hybridisation is that it incorrectly predicts the ultraviolet photoelectron spectra of ...
2
votes
0answers
40 views

Can stimulated Raman processes be strong enough to drive out of equilibrium?

In the (spontaneous) Raman process, incident light $\hbar \omega_1$ scatters and transfers some energy $\hbar \omega$ to a vibrational excitation of molecule or solid. Typically this is a very rare ...
3
votes
2answers
83 views

H-NMR with 10H integration?

I have the following two spectra (IR and 1H-NMR) see below. The chemical formula is: C16H16O2 Thus DBE = 9 My approach: From the IR, I can see that there's no broad peak around 2500-3300, thus I ...
0
votes
1answer
76 views

Does Mie Scattering occur in Liquid or is Rayleigh scattering?

Rayleigh scattering occurs when the dimensions of the scatter is much smaller than the wavelength of the incident electromagnetic radiation. Mie scattering occurs when the dimensions of the ...
8
votes
1answer
237 views

Empirical Evidence and Assignment of Orbital Energies (Electron Filling)

I see a lot of questions on electron configurations from students at various levels here. Students mechanically remember how to fill orbitals and sorry to say many teachers do the same. Not a single ...
0
votes
1answer
36 views

Size of atomic shells

Is the distance of some $n^{th}$ shell ($n$ $\neq$ outermost shell) from the nucleus of an atom different for different elements? If so, then how much is the difference or how could we calculate it?
2
votes
1answer
109 views

Spectroscopic Determination of an Equilibrium Constant [closed]

I got values of $\pu{5.0E-4}$, $\pu{2.5E-4}$, and $183$ for the following problems. However, these seem to be inaccurate and I'm not sure what to do. Here is the procedure: Obtain 6 disposable ...
4
votes
2answers
144 views

Raman Scattered (inelastic) photons rescattering outside of capture area

Imagine that you are focusing the raman laser right at the center of the vial sample with water (or any liquid) using 532nm laser. (from "Photometric Standards for Raman Spectroscopy) For raman 180 ...
4
votes
2answers
223 views

Determine structure from NMR

So I've come across this lovely spectrum of a compund where only its chemical formula is given with C5H9NO. I have made the pictures of the spectrum available below. obviously there is some pretty ...
1
vote
0answers
25 views

UV-Vis absorbtion spectra of a radical cation/anion. Is it different compared to its even counterpart?

I am studying gas-phase Uv-Vis spectra of radical molecules. If one electron is removed/captured from the neutral even electron molecule, what can I expect from the absorption spectra? Will new peaks ...
0
votes
0answers
37 views

What is the effect of applied magnetic field on absorption spectrum?

Upon application of a weak magnetic field, a line in the microwave absorption spectrum of rigid rotor splits into $3$ lines. The quantum number $(J)$ of the rotational energy level from which the ...
2
votes
1answer
327 views

Right Raman Spectrum of Cyclohexane

In this site, https://www.princetoninstruments.com/userfiles/files/assetLibrary/Technical%20posters/Poster-Aberration-Free-Raman-Spectroscopy-with-the-IsoPlane.pdf the raman spectrum of cyclohexane ...
1
vote
2answers
46 views

Size of target substance in IR and Raman Spectroscopy

Usually what is the size (in nanometer) of the sample or target substance in IR and Raman Spectroscopy? Which one has largest size of sample it can scan, how many molecules or atoms are involved? If ...
2
votes
1answer
154 views

Spectra from Dipole Moments [closed]

If there is a change in dipole moments such as absorption spectroscopy, there are infrared absorptions (and/or transmittance) corresponding to them. Is the reason change in dipole moments are in ...
8
votes
1answer
170 views

Any way to see “cubic-active” vibrational modes in molecules?

For molecular complexes with a moderate amount of symmetry there are usually vibrational modes that are neither infrared nor Raman active. Sometimes these modes transform as some cubic polynomial in x,...
2
votes
2answers
190 views

Why does the dipole moment of molecules go from positive to negative? [duplicate]

In physics the dipole moment is said to go from the negative to the positive pole, check for instance https://en.wikipedia.org/wiki/Electric_dipole_moment (Elementary definition). This makes sense ...
5
votes
1answer
924 views

Spectrometer vs Spectrometry vs Spectroscopy

How do you differentiate between the three? I read that "Spectrometry deals with the measurement of a specific spectrum. There are four primary types of spectrometers: Mass spectrometry 2. Neutron ...

1
2 3 4 5
12