1. MILLIMETER WAVE SPECTRUM OF NITROMETHANE
Vadim Ilyushin
Institute of Radio Astronomy of NASU, Kharkiv, Ukraine.

2. Previous work on the CH3NO2 rotational spectrum
[1] E. Tannenbaum, R.D. Johnson, R.J. Myers, W.D. Gwinn, J. Chem. Phys. 22 (1954) 949.
[2] E. Tannenbaum, R.J. Myers, W.D. Gwinn, J. Chem. Phys. 25 (1956) 42–47.
[3] A.P. Cox, S. Waring, K.Morgenstern, Nature Physical Science Vol. 229 (1971)
[4] L. Engelbrecht, D. Sutter, H. Dreizler, Z. Natruforsch 28a (1973)
[4] A.P. Cox, S. Waring, J. Chem. Soc., Faraday Trans. 2 (68) (1972) 1060–1071.
[5] F. Rohart, J. Mol. Spectrosc. 57 (1975) 301–311
[6] G.O. Sørensen, T. Pedersen, Stud. Phys. Theor. Chem. 23 (1983) 219–236.
[7] G.O. Sørensen, T. Pedersen, H. Dreizler, A. Guarnieri, A.P. Cox, J. Mol. Struct. 97 (1983) 77–82.
Previous Results in these papers: maximum frequency - 80 GHz, rotational quantum number range: J  29 and Ka  18.

3. Motivation V6  2 cm-1 = 3.46 D A = 13341 MHz B = 10545 MHz
100
200
300
400
500
600
700
800
900
cm-1
torsion m 1 2 3 4 5 6 7 8 9 10 11 12 13
(NO2)i
(NO2)o
(NO)s
(C-N)
SAV
V6  2 cm-1
= 3.46 D
A = MHz
B = MHz
C = 5876 MHz
B1/B2 and E1 type levels are not populated due to spin statistics
 = stretch;  = bend;  = rock; a = asymmetric; s = symmetric; i = in-plane; o = out-of-plane.
M.B. Dawadi, S. Twagirayezu, D.S. Perry, B. E. Billinghurst, J. Mol. Spectrosc. 315 (2015) 10–15

4. Modification of the RAM36 program
V. Ilyushin, Z. Kisiel, L. Pszczółkowski, H. Mäder, J. T. Hougen // J. Mol. Spectrosc. Vol. 259, pp (2010).
The RAM36 (rho-axis-method for 3 and 6-fold barriers) code realizes the Rho-axis-method approach for the molecules with the C3v top attached to a molecular frame of Cs or C2v symmetry and having 3- or 6-fold barrier to internal rotation respectively. The program carries out a global fit of rotational transitions in several torsional states simultaneously using a two step diagonalization procedure.

5. MW spectrometer in Kharkiv
BWO, 34 – 150 GHz
PLL
IF = 25 MHz
FM modulated synthesizer
25 MHz
Klystron 3.4 – 5.2 GHz
IF = 5 MHz
Absorbing cell
Amplifier
Lock-in detector
Sine wave synthesizer
7 – 120 KHz
DAC
DDS AD9851
30 – 60 MHz
Band-pass amplifier MHz
Synthesizer 360 MHz
Frequency divider f/2
Frequency Doubler (optional)
Detector Schottky
Reference synthesizer MHz

6. Portion of the recorded spectrum of CH3NH2 around 134 GHz.
133840
134280
134720
135160
MHz
Experiment
Prediction

7. Summary of the Least Squares Fit Torsional state Measurement Precision
m # Jmax rms(kHz) unc(kHz) # Jmax rms(kHz)   
 Overall rms: 25.9 kHz
Weighted rms: 0.89
Number of parameters: 93
m≠
Frequency range: 9 – 237 GHz (previous GHz )
Jmax =50, Kamax = 42 (previous Jmax = 29, Kamax = 18)
Number of lines: 5838 (correspond to 4478 torsion-rotation transitions previous number – less than 200)

8. Conclusions
A new study of the nitromethane (CH3NO2) spectrum in the millimeter wave frequency range up to 237 GHz has been carried out and a fit within experimental error has been achieved for the lowest 11 m torsional states of the molecule using the RAM approach.
The RAM36 program is now capable to treat quadrupole hyperfine structure due to one nucleus with nonzero quadrupole moment in the first order of perturbation theory.

9. Thank you for your attention