There are 7 files of supplementary material, including this file.
All files are text files.

This file, 1_Explan.txt, provides information on the content of the other files.

2_ND_2.fit is the output file of the fit of spectroscopic data used in the present study.
3_ND_2.lin is the corresponding line file.
4_ND_2.par is the corresponding parameter file. 
5_ND_2.cat is the output file of the prediction made with the parameters determined in this study.
6_ND_2.var is the corresponding parameter file
7_ND_2.int is the corresponding intensity file

These files are output file and input files of the spfit/spcat program 
by H. M. Pickett. The latest official version from 6 Nov. 2007 needs to be used.
Information on the program is available on the following JPL web site:
http://spec.jpl.nasa.gov/
A particularly helpful document is spinv.pdf

In addition, we recommend the following articles:
H. M. Pickett:
The fitting and prediction of vibration-rotation spectra with spin interactions
http://dx.doi.org/10.1016/0022-2852(91)90393-O
H. M. Pickett et al.:
Submillimeter, Millimeter, and Microwave Spectral Line Catalog
http://dx.doi.org/10.1016/S0022-4073(98)00091-0

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More details on    2_ND_2.fit 

Lines 1 to 65 display the initial parameters with variabilties and contraints
(see explanations to  4_MeCN_v8le2.par  for additional information)
Lines 66 to 182 provides information on internal blocks
Line 183 gives the maximum Dimension for Hamiltonian
Line 184 gives explanations to some of the following columns.
Lines 185 to 1116 gives all lines used in the fit.

The first column gives the line number followed by a colon.

The next 16 columns represent the quantum numbers. 
(see explanations to  3_ND_2.lin  for additional information)

The next two columns represent the experimental frequency 
followed by the calculated frequency. 
The units are in megahertz (MHz) or in inverse centimeters (cm-1), 
depending on the sign of the uncertainty. 
A negative sign indicates frequencies, uncertainties and residuals are 
in cm-1.

The next column gives the residuals between observed frequencies and those calculated 
from the final parameter set.

The next column gives the estimated uncertainties in units of MHz 
or cm-1.

The next column, which is the last one for unblended lines, 
gives the calculated uncertainties of the lines after each iteration. 
Here it is zero throughout, because there was only one iteration. 

In case of blended lines, the next three columns provide the weighted average 
of the calculated frequencies, the residuals between experimental frequencies 
and the average frequencies, and the weights of the blends.
The weights are usually the relative intensities.

Please note: each set of blended lines is treated as one piece of information. 
Blended lines are recognized as such only if the appear subsequently in the line list. 
The experimental uncertainties are those of the blend and 
should be equal for each contributing transition of the blend.

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More details on    3_ND_2.lin

The first 8 columns are the quantum numbers of the upper state.
The next 8 columns are the quantum numbers of the lower state.

The quantum numbers are J, Ka, Kc, the state number, J, F1, I_D and F, 
The last three quantum numbers only matter for transitions with 
resolved hyperfine structure. 
In the absence of hyperfine splitting, F = I_D = F1 = J, and F, I_D, and F1 are redundant. 
They need to be given for reasons of formatting consistency.

The state number is a counting number to designate if hyperfine structure is resolved.
State numbers 
0 refers to those transitions for which hyperfine structure was resolved
1 refers to those ones for which hyperfine structure was not resolved

The next column is the experimental frequency in units of MHz 
or in units of cm-1; 
the latter applies to negative uncertainties.

The next column is the estimated uncertainty in MHz 
or in cm-1. 
In case of blended lines, the relative weights are given next.

The source of each line is given in the last column; 
see references in the article for more details.

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More details on    4_ND_2.par and 6_ND_2.var

The first line gives the title and the date.
The second line gives number of parameters and lines (minus sign allow to use up to 10 quanta per state). 
Lines 3 and 4 describe the different "states" (see above).
3332 and 2 refer to asymmetric top quanta with and without hyperfine splitting.
The next column indicates the total number of states in line 3 
and the respective state number in all following lines. 
K_min and K_max follow. 
0 signals consider all off-diagonal interactions. 
See spinv.pdf or http://www.astro.uni-koeln.de/cdms/pickett for further details on the next columns.

All subsequent lines give
- parameter code (a negative value signals keep ratio with previos parameter) 
- parameter value (in units of MHz), 
- variability (a large number signal vary as much as needed, a small number signal fixed value) in the 4_ND_2.par file
or uncertainty of the paramater in the 4_ND_2.var file.
- The meaning of a parameter is given after the slash.

The last 2 digits of the parameter code indicate the states for which the parameter is defined.
99 refers to all states.

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More details on    5_ND_2.cat

Each lines have the same format:

The first 13 digits give the line frequency in MHz

The next 8 digits give the estimated experimental error in MHz

The next 8 digits give the base 10 logarithm of the integrated intensity in units of nm MHz

The next 2 digits give the degrees of freedom in the rotational partition function (0 for atoms, 2 for linear molecules, 
and 3 for nonlinear molecules)

The next 10 digits give the lower state energy in cm-1

The next 3 digits indicate the upper state degeneracy

The next 7 digits give the species tag

The next 4 digits identify the format of the quantum numbers given in the next field.

The next 32 digits identify the quantum numbers for the upper and lower states.

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More details on    6_ND_2.int

The first line contains the title and the date

The second line gives the rotational partition function (third parameter) as well as 
the frequency range of the .cat file and the rotational temperature (last parameter)

The following lines gives the value of each component of the dipole moment 



