8. Overview of the most important VNMRJ parameters

There are well over a hundred parameters in VNMR. Some are of very little importance to the routine user. Only acquisition parameters are listed in the sequence as they appear in the parameter window and/or in a parameter printouts.

8.1 1D Data acquisition  (i300, i400, s400, m400, ibd5, u500, i600)


typical values





i300: 299.961
i|m400: 399.798
u500: 499.849
i600: 599.932
spectrometer frequency

basic Larmor frequency, depends on spectrometer; cannot be set by user
tn H1

C13, N15, P31

transmitter nucleus

always H1 on i300 and i600; other nuclei possible on i400, m400, ibd5 and u500


1D: 2.0 or more

2D: 0.2 to 0.8

acquisition time

length of FID; determines digital resolution
digital resolution = 1/at (without zero-filling)

note: at = np/(2*sw)



i300: 14,400
i|m400: 19,200
u500: 24,000
i600: 28,800
number of data points
more needed at higher fields to maintain digital resolution 

note: at = np/(2*sw)



i300: 3600
i|m400: 4800
u500: 6000
i600: 7200
sweep width
more needed at higher fields to cover 12 ppm range

note: at = np/(2*sw)



not used filter bandwidth

often replaced by DSP, therefore ‘not used’

bs 4-8 block size

number of transients after which data are sent from the console to the host computer

ss 2-4 steady-state pulses (also known as dummy scans)

number of complete executions of the pulse sequence prior to actual data collection



59 (or less), other values common for special techniques transmitter power level

Note: for every 6 dB down, pw doubles



5 to 15 pulse width

length of a radio frequency pulse to rotate magnetization from z to xy-plane; depends on probe, tpwr, spectrometer



0 length of additional pulse(s) in the sequence

often not used



3.0 in 1D

0.8 to 1.2 in 2D

1st delay

relaxation time; allowing the magnetization to return to the z direction



  transmitter offset

solvent and field dependent



16-32 receiver gain

sensitivity of the receiver; too high causes ADC overflow and serious baseline distortions

Note: for every 6 dB increase, the sensitivity doubles

nt 1, 2, 3, 4…

4, 8, 16, 32, 64…

number of transients

signal-to-noise increases with root_nt.gif (936 bytes); usually multiples of 4 or 8 required except for gradient-enhanced techniques where any integer is possible; for indefinite acquisition (runs until stopped by aa) enter 1e9

ct  -- completed transients

cannot be changed by user; if exp. runs to completion then ct = nt

seqfil s2pul, aogcosy, gHMQC…. name of the pulse sequence's file name

s2pul is used for standard 1D spectra


date  -- date the spectrum is recorded (not processed)

entered automatically by the system

solvent d2o, cdcl3, cd3od, cd2cl2… lock solvent

directly affects tof and referencing of spectrum; read in with parameter sets and should not be changed unless solvent is not in the list

D2O and d2o etc. are identical (only for this parameter; this is an exception under UNIX!)

file exp
real filename
file name of parameter set or data file

reads exp when an experiment is complete; when data are saved and read back, file shows the full name including the path


dn H1, C13, N15 decoupler nucleus

H1 for homonuclear exp.
C13 or N15 for gHMQC and similar exp.



  decoupler offset

for solvent presaturation set to solvent resonance; for heteronuclear decoupling set to middle of frequency range of decoupled nucleus; both depends on the field and the solvent (i.e. the lock frequency)

dm nnn, ynn, nny… decoupler mode

pulse sequences are divided into several time intervals (many have 3) and each letter defines whether the decoupler is on (at frequency dof and power dpwr) or off in the respective time interval

‘n’ for no decoupling, ‘y’ turns the decoupler on

dmm c, w, g… decoupler modulation mode

for presaturation of solvent ‘c’; for broadband decoupling of entire nucleus ‘w’ (WALTZ) or ‘g’ (GARP)

dmf   decoupler modulation frequency

inactive for dmm=’c’



-16 to 45 decoupler power level

controls the power level of the decoupler channel; depends on solvent (for presaturation) and band width for heteronuclear broadband decoupling which is a function of the field strength

Note: for every 6 dB up, the power doubles

homo ‘y’ or ‘n’ homodecoupling control

‘y’ for homonuclear decoupling, ‘n’ for heteronuclear decoupling, both require ‘y’ in the correct place of dm to turn the decoupler actually on

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