4P-012

A Study on possibility of observing “ortho-para” microwave transition in Disulfur
Dichloride,(Tokyo Institute of Technology) Zeinab Dehghani Tafti, Shinji Ota, Asao Mizoguchi,
HidetoKanamori

1. Introduction

One of the special properties of S l is being a candidate for observing “ortho-para” transition.
3
As two identical Cl atoms in S l have 𝐼𝑖 = nuclear spin, the total nuclear spin angularmomentum can be 𝐼 =. According to Pauli principle, molecular levels in S l are=rotational states coupled withclassified to ortho or para levels. The former is
odd-I nuclear spin states and the latter is=and even-I. In general, the transition
between ortho and para states is strictly forbidden. But an interaction, which makes pureortho levels mix with pure para states and vice versa, can make the “ortho-para” transition
possible. As an example, if an initial ortho state; 𝑖 ⟩ in a transition is superimposed with apara state; | 𝑖 ⟩ and the final state is an ortho; | ⟩ state, we can estimate the intensity of theforbidden transition by the equation as below [1]:𝐼 = |⟨𝑖𝑖| |⟩| =|⟨ 𝑖 | |⟩| =𝑖|⟨||𝑖𝑖|𝑖|

⟩||⟨

𝑖| |

⟩|It means that the forbidden transition intensity can be obtained from an intensity borrowing.
from the corresponding allowed transition;⟨ 𝑖 | | ⟩ by a factor of
Until now such a kind of “ortho-para” transition has never been experimentally observed [1].
Recently, Mizoguchi et al. studied cm-FTMW spectroscopy of S l for
quantum numbers
and found some evidences of ortho-para mixing due to quadrupole hyperfine interaction[2].
However, the mixing ratio is not so large enough to detect the “ortho-para” transition in the cmMW region. Generally speaking, spectral intensity becomes stronger as increase of the transition
frequency, the searching the forbidden transition at higher frequencies is advantageous. So we
extended the MW spectroscopic measurements of S l from cm to mm wave regions in orderto get more information on the ortho-para mixing coefficients of higher and rotational states.
Using our new rotational molecular constants, we can calculate the ortho-para mixing
coefficients for all the states and found the best candidates for detecting “ortho-para”
transitions.

2. Experiment
We extend the observation of S l up to 100 GHz by using a mm-MW spectrometer
combined with a pulsed jet nozzle with a repetition frequency of 10Hz. To make the rotationaltemperature as low as 10K, 0.5 atm Ar was used as the buffer gas. The MW form a multiplied
synthesiser was detected by an InSb detector cooled by liquid Helium. A gated data acquisition
system with source frequency modulation technic was used. We also observed some lines bygas cell experiment with a temperature of 200K in order to get information about higher
rotational states.

3. Result and Discussion

We observed 70 transitions for S 3 l and 80 transitions for S 3 l3 l in the frequency regionof 75GHz to 100GHz and for quantum numbers less than = . Based on these observation wedetermined new rotational molecular constants including the fourth and sixth order centrifugal
distortion constants by a least square method, as shown in Table 1.

By these new molecular constants we had the chance of investigating interactions between
levels with different ortho or para symmetry. As the total angular quantum number;=𝐼
𝐼 is always good quantum number, we finding out the largest mixing statesby hitting every Eigen vectors in each F block. Our study shows the highest ortho-para mixing
coefficients belongs to K doubling levels with == . The next considerable ortho=. We also foundpara mixing coefficients were found between levels with =ortho-para mixing between levels with accidental relationships between their rotational
quantum numbers. Table 2 shows the examples from these three groups of mixed levels.
Figure 1 shows our candidate for “ortho-para” transition which starts from mostly “ortho”
𝑖𝑖state;=𝐼=. This “ortho” state is mixed with a para state;3𝑖=with the mixing coefficient;=. So if we calculate a R-transition
between this state and=, which is very little mixed with ortho states, the3“ortho-para” transition between
andby intensity equal to 0.17 of that3
3of the allowed transition of. The result is drawn in red stick line in3
Figure 1. However, there are several allowed transitions located around the “ortho-para”
transition. The transition frequency is about 1.4MHz away from the nearest allowed transition
which shown in the figure1. This value is larger than Doppler broadening (1MHz) in ourexperimental condition. So detection ofthis “ortho-para” transition seems
feasible with normal spectroscopic
technics.
Table 1.The rotational constants and centrifugal distortion constants of S l/MHz5533.8933 (15)a5533.8964 (11)

/MHz
/MHz
/kHz
/kHz
/kHz
/kHz
/kHz
/Hz

1393.8509 (14)1232.6642 (16)0.584 (5)-5.217 (40)24.01 (5)0.123 (5)4.7 (8)0.032 (4)1393.8436 (3)1232.6728 (2)0.556 (3)-5.115 (28)24.70 (25)0.144 (2)

/Hz
/Hz
/Hz
/Hz
/Hz
/Hz

-1.3 (6)4 (2)-4 (2)-0.014 (3)3.6 (4)-41(21)Figure 1. predicted spectrum pattern of one of the candidates for observing “ortho-para” transitions. blue lines
shows normal transitions and red lines shows “ortho-para” transition.

Table 2. Example of three types of mixed levels
Relation
betweeninteracting levels====
accidental

Main part of wave
function,𝐼

Mixed part of wave
function,𝐼

Mixingcoefficient,

30.17
0.008

1.1249100312.8397

30.002

256.7134

References
1.A.Miani,J.Tennyson, J.Chem.Phys.120,2732,(2004)
2.A.Mizoguchi,Sh.Ota, H.Kanamori,Y.Sumiyoshi, Y.Endo, J.Mol.Spect, 250,86,(2008)