Frequency lists

Frequency lists are used in NMR experiments to specify arrays of frequencies for selective excitation, CEST, or other variable-frequency experiments. On Bruker spectrometers, these are stored in files like fq1list through fq8list.

NMRTools represents frequency lists as FQList structures that preserve encoding information (Hz vs ppm, relative vs absolute) and provide safe conversion functions.

Encoding

Frequency lists can be specified on the spectrometer in several ways: in Hz or ppm, and relative to the carrier or to the base frequency (0 ppm). An FQList stores the values with their unit and whether they are relative, and, once attached to a channel with withreference, the base and carrier frequencies needed to convert them. The raw values are returned by data(fqlist), but ppm and hz should be used to read frequencies, since they apply the encoding.

Accessing frequency lists

Frequency lists are automatically imported when loading data:

# Load CEST experiment
spec = loadnmr("path/to/cest/experiment")

# Get frequency list
fqlist = acqus(spec, :fq1list)

Extracting frequency values

Use ppm() and hz() to safely extract frequency values. These functions handle all unit conversions automatically.

Get chemical shifts (in ppm)

dim = dims(spec, F2Dim)
ppm_values = ppm(fqlist, dim)

Get offsets from carrier (in Hz)

dim = dims(spec, F2Dim)
offset_hz = hz(fqlist, dim)

Creating frequency lists

Construct FQList objects programmatically:

using NMRTools

# Frequency list in Hz, relative to carrier
fq_rel = FQList([100.0, 200.0, 300.0], :Hz, true)

# Frequency list in ppm, absolute (chemical shifts)
fq_abs = FQList([7.5, 8.0, 8.5], :ppm, false)

3-element FQList{Float64}:
 7.5
 8.0
 8.5