Hyperfine-resolved transition frequency list of fundamental vibration bands of H35Cl and H37Cl

Journal of Molecular Spectroscopy 306 (2014) 19–25

Contents lists available at ScienceDirect

Journal of Molecular Spectroscopy journal homepage: www.elsevier.com/locate/jms

Hyperfine-resolved transition frequency list of fundamental vibration bands of H35Cl and H37Cl Kana Iwakuni ⇑, Hideyuki Sera, Masashi Abe, Hiroyuki Sasada Department of Physics, Faculty of Science and Technology, Keio University, 3-14-1, Hiyoshi, Kohoku-ku, Yokohama 223-8522, Japan

a r t i c l e

i n f o

Article history: Received 13 September 2014 Available online 16 October 2014 Keywords: HCl Mid-infrared Hyperfine structure Sub-Doppler resolution Optical frequency comb DFG

a b s t r a c t Sub-Doppler resolution spectroscopy of the fundamental vibration bands of H35Cl and H37Cl has been carried out from 87.1 to 89.9 THz. We have determined the absolute transition frequencies of the hyperfine-resolved R(0) to R(4) transitions with a typical uncertainty of 10 kHz. We have also yielded six molecular constants for each isotopomer in the vibrational excited state, which reproduce the determined frequencies with a standard deviation of about 10 kHz. Ó 2014 Elsevier Inc. All rights reserved.

1. Introduction Hydrogen chloride molecules have an intense fundamental vibration band around 2900 cm1. They play an important role for astrophysics [1,2] and atmospheric chemistry [3,4]. The large rotational constant allows us to record a rotation-resolved absorption spectrum even with grating and low-resolution FTIR spectrometers. Therefore, the fundamental band spectrum of HCl appears in a number of textbooks and is taken up in laboratory experiments as a typical rotation-vibration band of diatomic molecules. However, the extensively spread band caused by the large rotational constant requires widely tunable sources. It has therefore been difficult to apply laser spectroscopy to HCl. The R(2) and P(14) transitions were recorded by tunable diode lasers to investigate collisional processes [5], but sub-Doppler resolution infrared spectra have not been recorded. The most accurate transition frequencies were provided with FTIR [6]. However, the molecular constants were determined in conjunction with the results of emission spectroscopy [7]. Molecular-beam radio-frequency spectroscopy of HCl was carried out for the v = 0, 1, and 2 states, and the hyperfine structure of chlorine and hydrogen nuclei was precisely analyzed [8,9]. Rotational spectra of the ground state were recorded in millimeter-wave and sub-millimeter-wave spectroscopy up to 9 THz[10–13], whereas the quadrupole hyperfine structure caused by the chlorine nucleus was resolved only in the low-J transitions. A sub-Doppler

resolution rotational spectrum was recorded for the R(0) transition, and the magnetic hyperfine structure caused by the hydrogen nucleus was completely resolved [14]. Subsequently, the improved molecular constants in the ground state were reported [15]. Doppler-limited rotational spectrum of the v = 1 state was recorded by tunable FTIR spectroscopy[16]. In this paper, we have applied our spectrometer, which consists of a widely tunable difference-frequency-generation (DFG) source, an enhanced-cavity absorption cell (ECAC), and an Er-fiber-laserbased optical frequency comb (OFC), to sub-Doppler resolution spectroscopy of HCl. The spectral resolution is about 250 kHz, which is higher than that of Doppler-limited rotational spectroscopy. We have resolved the quadrupole hyperfine components including cross-over resonances of the R(0) to R(4) transitions of H35Cl and H37Cl in the fundamental vibration band and measured the absolute transition frequencies with an uncertainty of about 10 kHz. The sensitivity of the spectrometer is not high enough to observe all weak hyperfine transitions with DF = 0 and 1, but the cross-over resonances provide information for some of the missing transitions. Here, F is the total angular momentum quantum number. The molecular constants of the vibration excited state are determined while those of the ground state are fixed at the values acquired in sub-millimeter spectroscopy [15]. 2. Theory The Hamiltonian for analysis is given by

⇑ Corresponding author. E-mail address: [email protected] (K. Iwakuni). http://dx.doi.org/10.1016/j.jms.2014.09.013 0022-2852/Ó 2014 Elsevier Inc. All rights reserved.

H ¼ Hvib þ Hrot þ Hquad þ Hmagnetic ;

ð1Þ

20

K. Iwakuni et al. / Journal of Molecular Spectroscopy 306 (2014) 19–25 0.15

0.06

(a) R (0)

0.05

0

−0.05

−0.1

−0.15

(b) R (1)

0.04

Signal (arb. unit)

Signal (arb. unit)

0.1

0.02

0

−0.02

−0.04

0

5

10

15

20

25

30

−0.06

35

0

Frequency / MHz - 87 127 054. 572 7

10

20

30

40

50

Frequency / MHz - 87 716 131.091 6 0.4

0.1

(c) R (2)

0.2

Signal (arb. unit)

0.05

Signal (arb. unit)

(d) R (3)

0.3

0

−0.05

0.1 0 −0.1 −0.2 −0.3

−0.1 0

10

20

30

40

50

Frequency / MHz - 88 286 249. 373 6

−0.4

0

10

20

30

40

Frequency / MHz - 88 837 027. 207 3

0.2 0.15

(e) R (4)

Signal (arb. unit)

0.1 0.05 0 −0.05 −0.1 −0.15 −0.2 −0.25

0

10

20

30

40

Frequency / MHz - 89 368 108. 637 2 Fig. 1. Absorption lines of H35Cl acquired with the OFC-based DFG spectrometer. Arrows indicate crossover resonances. (a) R(0), (b) R(1), (c) R(2), (d) R(3) and (e) R(4) transitions.

where Hvib ; Hrot ; Hquad , and Hmagnetic are Hamiltonians of vibration, rotation, the quadrupole hyper-fine interaction of the chlorine nucleus, and the magnetic hyperfine interaction between the chlorine nucleus and the magnetic field produced by the molecular rotation. The diagonal elements of the first two terms are expressed as

< v jHvib jv >¼ T v

ð2Þ

and

< v ; JjHrot jv ; J >¼ Bv JðJ þ 1Þ  Dv ½JðJ þ 1Þ2 þ Hv ½JðJ þ 1Þ3 þ Lv ½JðJ þ 1Þ4 ;

ð3Þ

where v and J are the vibrational and rotational quantum numbers, T v is the vibrational term value, Bv is the rotational constant, Dv is the centrifugal distortion constant, and Hv and Lv are the higherorder centrifugal distortion constants. The diagonal elements of the third term are given by

< v ; J; FjHquad jv ; J; F >¼ ðeqQ Þv f ðI; J; FÞ;

ð4Þ

where I is the nuclear spin quantum number which is 3/2 for H35Cl and H37Cl, F = I + J is the total angular momentum, I is the nuclear spin angular momentum, and J is the rotational angular

21

K. Iwakuni et al. / Journal of Molecular Spectroscopy 306 (2014) 19–25 0.1 0.04

(a) R (0)

(b) R (1)

0.05

Signal (arb. unit)

Signal (arb. unit)

0.02 0

−0.05

0

−0.02 −0.1 −0.04 −0.15

0

5

10

15

20

25

30

0

35

0.06

20

30

40

50

0.3

0.04

(d) R (3)

0.2

(c) R (2)

0.1

0.02

Signal (arb. unit)

Signal (arb. unit)

10

Frequency / MHz - 87 651 241. 860 7

Frequency / MHz - 87 063 018. 715 2

0

−0.02

0 −0.1 −0.2

−0.04 −0.3 −0.06

0

10

20

30

40

50

0

10

20

30

40

Frequency / MHz - 88 770 555. 386 5

Frequency / MHz - 88 220 540. 542 8 0.2 0.15

(e) R (4)

Signal (arb. unit)

0.1 0.05 0 −0.05 −0.1 −0.15 −0.2

0

10

20

30

40

50

60

Frequency / MHz - 89 300 901. 023 2 Fig. 2. Absorption lines of H37Cl acquired with the OFC-based DFG spectrometer. Arrows indicate crossover resonances. (a) R(0), (b) R(1), (c) R(2), (d) R(3) and (e) R(4) transitions.

momentum. Here, ðeqQ Þv is the quadrupole coupling constant, and f(I; J; F) is the Casimir’s function given by 3 CðC 4

þ 1Þ  IðI þ 1ÞJðJ þ 1Þ f ðI; J; FÞ ¼ 2Ið2I  1Þð2J  1Þð2J þ 3Þ

ð5Þ

and

C ¼ FðF þ 1Þ  JðJ þ 1Þ  IðI þ 1Þ:

ð6Þ

The diagonal elements of the last term is expressed as

< v ; J; FjHmagnetic jv ; J; F >¼ C Clv I  J ¼ C Clv ½FðF þ 1Þ  IðI þ 1Þ  JðJ þ 1Þ=2;

ð7Þ

where C Clv is the magnetic coupling constant. The magnetic interaction caused by the hydrogen nucleus is not considered here because the spectral resolution is not high enough to evaluate it.

22

K. Iwakuni et al. / Journal of Molecular Spectroscopy 306 (2014) 19–25

Table 1 Measured transition frequencies for H35Cl. F0

J0

F 00

J 00

3/2 3/2 3/2 5/2 5/2 1/2

1 1 1 1 1 1

3/2 3/2 3/2 3/2 3/2 3/2

0 0 0 0 0 0

3/2 5/2 3/2 5/2 5/2 3/2 3/2 1/2 5/2 7/2 5/2 3/2 1/2 5/2

2 2 2 2 2 2 2 2 2 2 2 2 2 2

1/2 5/2 1/2 5/2 5/2 1/2 5/2 1/2 3/2 5/2 3/2 3/2 1/2 3/2

1 1 1 1 1 1 1 1 1 1 1 1 1 1

7/2 7/2 7/2 5/2 3/2 7/2 9/2 5/2 7/2 5/2 3/2 5/2 3/2

3 3 3 3 3 3 3 3 3 3 3 3 3

7/2 7/2 7/2 3/2 1/2 5/2 7/2 3/2 5/2 3/2 1/2 5/2 3/2

2 2 2 2 2 2 2 2 2 2 2 2 2

9/2 9/2 9/2 7/2 5/2 9/2 11/2 7/2 9/2 7/2 7/2 5/2 5/2

4 4 4 4 4 4 4 4 4 4 4 4 4

9/2 9/2 9/2 5/2 3/2 7/2 9/2 5/2 7/2 7/2 5/2 3/2 5/2

3 3 3 3 3 3 3 3 3 3 3 3 3

11/2 11/2 9/2 7/2 11/2 13/2 9/2 11/2 9/2 7/2

5 5 5 5 5 5 5 5 5 5

11/2 11/2 7/2 5/2 9/2 11/2 7/2 9/2 7/2 5/2

4 4 4 4 4 4 4 4 4 4

F0

J0

F 00

J00

5/2 1/2

1 1

3/2 3/2

0 0

1/2

1

3/2

0

1/2 5/2 7/2 3/2 7/2

2 2 2 2 2

1/2 3/2 5/2 3/2 5/2

1 1 1 1 1

3/2

2

3/2

1

1/2 1/2

2 2

3/2 3/2

1 1

7/2 9/2

3 3

5/2 7/2

2 2

5/2 5/2 3/2 3/2

3 3 3 3

5/2 5/2 3/2 3/2

2 2 2 2

9/2 11/2

4 4

7/2 9/2

3 3

7/2 7/2

4 4

7/2 7/2

3 3

5/2 5/2

4 4

5/2 5/2

3 3

11/2 13/2

5 5

9/2 11/2

4 4

9/2 9/2 7/2 7/2

5 5 5 5

9/2 9/2 7/2 7/2

4 4 4 4

Obs. (kHz)

Obs.  Cal. (kHz)

87 87 87 87 87 87

127 127 127 127 127 127

059 068 075 076 083 090

436.2(51) 168.8(45) 000(30) 904.6(64) 708(15) 523.0(61)

2.3 1.5 17.8 2.1 10.2 7.6

87 87 87 87 87 87 87 87 87 87 87 87 87 87

716 716 716 716 716 716 716 716 716 716 716 716 716 716

141 142 150 151 151 157 157 159 159 160 166 172 174 174

854.3(43) 932.2(51) 468.5(56) 636(33) 636(33) 041(20) 821(37) 095.1(75) 969.3(33) 465.0(38) 087.8(27) 201.4(32) 255(15) 697(15)

1.2 1.8 2.9 182.4a 63.8a 14.1 7.9 5.4 4.0 0.7 0.8 0.6 8.6 8.4

88 88 88 88 88 88 88 88 88 88 88 88 88

286 286 286 286 286 286 286 286 286 286 286 286 286

255 264 264 268 268 272 272 274 276 276 276 280 285

311.1(85) 038(39) 038(39) 350.9(28) 707.7(49) 409.5(25) 910.7(42) 334(12) 351.7(29) 998(23) 998(23) 292.5(68) 535.2(64)

10.2 170.9a 77.9a 1.8 1.4 4.9 1.3 10.9 2.0 56.8a 120.0a 0.4 4.9

88 88 88 88 88 88 88 88 88 88 88 88 88

837 837 837 837 837 837 837 837 837 837 837 837 837

031 039 039 046 046 048 048 050 051 054 055 055 063

178(51) 888.7(94) 888.7(94) 429.6(42) 771.7(53) 321.1(15) 828.1(44) 279.8(72) 229.3(81) 164(16) 080.3(58) 080.3(58) 558(20)

0.6 136.1a 115.3a 5.5 11.9 5.0 0.8 5.6 1.5 28.0 85.7a 88.4a 4.3

89 89 89 89 89 89 89 89 89 89

368 368 368 368 368 368 368 368 368 368

120 120 127 128 128 129 130 131 136 136

325(23) 325(23) 676.9(70) 019.1(40) 794.7(74) 308.9(11) 481(40) 090(16) 298(16) 298(16)

130.6a 123.4a 5.9 4.7 0.2 6.6 32.6 14.9 96.7a 74.9a

Obs.: Observed frequency; Obs.  Cal.: Observed frequency minus calculated frequency. a Unweighted for fitting.

3. Comb-referenced DFG spectrometer Experimental setup is similar to that in the previous paper [17]. Pump and signal sources for DFG are a 1.06-lm Nd:YAG laser and a 1.55-lm extended-cavity laser diode (ECLD). The pump and signal waves are combined and lead to a waveguide-type periodically poled lithium niobate (PPLN), which generates the 3.4-lm idler wave with a nominal conversion efficiency of 10%/W. The power levels of the pump, signal, and idler waves are actually 100 mW, 50 mW, and 50 lW due to the coupling loss. Quasi-phase matching

is achieved by controlling the temperature of the PPLN. Two PPLNs are used to cover the frequency range from 86.4 to 90.1 THz, where there are the R(0) to R(5) transitions in the fundamental vibration band of H35Cl and H37Cl. The idler wave enters an ECAC, which consists of two 99.0% reflectors separated by 23.6 cm. The optical field strength is enhanced by about 20 times at the anti-node, and the effective absorption length is also increased by about 200 times. The ECAC is filled with natural-abundant HCl sample gas. The sample pressure is estimated at a few millitorr, which slowly decreases because HCl adsorbs to the glass surface of the ECAC.

23

K. Iwakuni et al. / Journal of Molecular Spectroscopy 306 (2014) 19–25 Table 2 Measured transition frequencies for H37Cl. F0

J0

F 00

J 00

3/2 3/2 3/2 5/2 5/2 1/2

1 1 1 1 1 1

3/2 3/2 3/2 3/2 3/2 3/2

0 0 0 0 0 0

3/2 5/2 3/2 5/2 5/2 3/2 3/2 1/2 5/2 7/2 5/2 3/2 1/2 5/2

2 2 2 2 2 2 2 2 2 2 2 2 2 2

1/2 5/2 1/2 5/2 5/2 1/2 5/2 1/2 3/2 5/2 3/2 3/2 1/2 3/2

1 1 1 1 1 1 1 1 1 1 1 1 1 1

7/2 7/2 7/2 5/2 3/2 7/2 9/2 5/2 7/2 5/2 3/2 5/2 3/2

3 3 3 3 3 3 3 3 3 3 3 3 3

7/2 7/2 7/2 3/2 1/2 5/2 7/2 3/2 5/2 3/2 1/2 5/2 3/2

2 2 2 2 2 2 2 2 2 2 2 2 2

9/2 9/2 9/2 7/2 5/2 9/2 11/2 7/2 9/2 7/2 7/2 5/2 5/2

4 4 4 4 4 4 4 4 4 4 4 4 4

9/2 9/2 9/2 5/2 3/2 7/2 9/2 5/2 7/2 7/2 5/2 3/2 5/2

3 3 3 3 3 3 3 3 3 3 3 3 3

11/2 11/2 9/2 7/2 11/2 13/2 11/2 9/2 7/2

5 5 5 5 5 5 5 5 5

11/2 11/2 7/2 5/2 9/2 11/2 9/2 7/2 5/2

4 4 4 4 4 4 4 4 4

F0

J0

F 00

J 00

5/2 1/2

1 1

3/2 3/2

0 0

1/2

1

3/2

0

1/2 5/2 7/2 3/2 7/2

2 2 2 2 2

1/2 3/2 5/2 3/2 5/2

1 1 1 1 1

3/2

2

3/2

1

1/2 1/2

2 2

3/2 3/2

1 1

7/2 9/2

3 3

5/2 7/2

2 2

5/2 5/2 3/2 3/2

3 3 3 3

5/2 5/2 3/2 3/2

2 2 2 2

9/2 11/2

4 4

7/2 9/2

3 3

7/2 7/2

4 4

7/2 7/2

3 3

5/2 5/2

4 4

5/2 5/2

3 3

11/2 13/2

5 5

9/2 11/2

4 4

9/2 7/2 7/2

5 5 5

9/2 7/2 7/2

4 4 4

Obs. (kHz)

Obs.  Cal. (kHz)

87 87 87 87 87 87

063 063 063 063 063 063

027 034 039 040 046 051

149.0(31) 033.5(18) 401(10) 918.0(18) 285.8(34) 653.6(40)

1.2 2.4 7.4 0.0 1.3 5.9

87 87 87 87 87 87 87 87 87 87 87 87 87 87

651 651 651 651 651 651 651 651 651 651 651 651 651 651

253 254 260 261 261 265 266 267 267 268 272 277 279 279

657.0(58) 497.3(45) 437(11) 369(18) 369(18) 636(32) 210(15) 234.0(84) 947(17) 330.5(23) 753.6(52) 570.8(63) 190(23) 546.8(13)

1.9 5.2 7.6 149.2a 44.0a 24.9 18.3 0.9 10.3 7.7 1.6 3.1 1.2 4.8

88 88 88 88 88 88 88 88 88 88 88 88 88

220 220 220 220 220 220 220 220 220 220 220 220 220

553 560 560 564 564 567 567 568 570 571 571 573 577

936(30) 839(11) 839(11) 225.6(57) 489(13) 432.1(49) 830.3(10) 952(11) 528.7(72) 039.3(72) 039.3(72) 640(17) 763(16)

18.3 145.3a 49.6a 6.0 19.8 0.7 7.7 18.3 5.4 41.9a 96.5a 5.0 0.5

88 88 88 88 88 88 88 88 88 88 88 88 88

770 770 770 770 770 770 770 770 770 770 770 770 770

561 568 568 573 573 574 575 576 577 579 580 580 586

356(21) 238.3(44) 238.3(44) 505.1(89) 505.1(89) 890.0(33) 288.7(24) 427.2(50) 175.7(40) 468(11) 202.2(97) 202.2(97) 898(18)

11.7 109.3a 87.2a 104.1a 169.3a 0.6 4.9 3.9 0.3 6.5 59.3a 77.4a 13.6

89 89 89 89 89 89 89 89 89

300 300 300 300 300 300 300 300 300

925 925 931 931 932 932 934 938 938

851(25) 851(25) 744.3(33) 744.3(33) 762(17) 762(17) 275(28) 429(29) 429(29)

151.7a 46.5a 145.1a 125.1a 278.8a 117.7a 1.4 111.5a 23.5a

Obs.: Observed frequency; Obs.  Cal.: Observed frequency minus calculated frequency. a Unweighted for fitting.

The pump and signal frequencies are respectively phase-locked to the nearest mode of the OFC. The 67 MHz repetition rate is locked to a synthesizer linked to the International Atomic Time (TAI) through the global positioning system (GPS). Therefore, the idler frequency is eventually stabilized to the TAI and then swept by changing the repetition rate of the OFC with the pump and signal frequencies following due to the servo locking. The mode frequency of the ECAC is locked to the idler frequency by the Pound–Drever–Hall method. This system is based on the absolute frequency, so it is possible to accumulate spectral data for a long

time without any frequency drift. In addition, wavelength-modulation spectroscopy at 3 kHz is applied to enhance the sensitivity.

4. Result and discussion Figs. 1 and 2 present observed spectra of the R(0) to R(4) transitions of H35Cl and H37Cl. The horizontal axis is scaled by the absolute frequency. The repetition rate of the OFC is swept in steps of 0.01 Hz corresponding to 13.1 kHz in the mid-infrared frequency.

24

K. Iwakuni et al. / Journal of Molecular Spectroscopy 306 (2014) 19–25

Table 3 Determined and fixed molecular constants for H35Cl and H37Cl.

T 1  T 0 (kHz) B1 (MHz) D1 (MHz) H1 (kHz) L1 (Hz) ðeqQ Þ1 (MHz) C Cl1 (kHz) B0 (MHz) D0 (MHz) H0 (kHz) L0 (Hz) ðeqQ Þ0 (MHz) C Cl0 (kHz)

H35Cl

H37Cl

86 519 385 472.5(68) 303 875.202 6(19) 15.632 11(14) 0.483 3(29) 0a 69.301(12) 59.03(49) 312 989.278 78b 15.831 346b 0.500 29b 0.024 30b 67.617 6b 54.00b

86 456 249 166.3(69) 303 425.644 6(20) 15.584 91(16) 0.476 2(35) 0a 54.608(14) 48.10(66) 312 519.100 33b 15.783 562b 0.498 08b 0.024 16b 53.288 1b 44.75b

Subscripts 0 and 1 indicate molecular constants of the vibrational ground and v = 1 states. a These are fixed at zero. b These are fixed at the values determined by Cazzoli [15].

Each spectrum is averaged over 16 to 20 sweeps, and each takes around 20 min to record. The idler frequency is swept by changing the repetition rate of the OFC, and the sweep range is limited to 130 MHz by the tuning range of the Nd:YAG laser. This is still wide enough to record the hyperfine components of the R(1) transition of H35Cl, which is spread most widely over 33 MHz. When two transitions share a common upper or lower level, a crossover resonance is generated at the middle frequency of these transitions with an intermediate intensity between them. This resonance is represented by arrows in Figs. 1 and 2. Therefore, even though no weak DF = 1 components are observed except for the R(0) transitions for each isotopomer, crossover resonances associated with the DF = 1 components of the R(1) to R(4) transitions for H35Cl and those of the R(1) to R(3) transitions for H37Cl are indeed observed. Each spectral line is recorded at least twice and fit to the first derivative of the Lorentz function with adjustable parameters for the center frequency, the amplitude, the linewidth, and the background offset. Tables 1 and 2 list the determined transition frequencies of H35Cl and H37Cl together with the uncertainties determined from the fitting and the scattering among the recorded spectra. F 0 and J 0 are the total and rotational angular momentum quantum numbers of the upper state, and F 00 and J 00 are those of the lower state. Rows presenting two transitions depict the crossover resonances between them. The transition frequencies are listed in frequency order where the number in parentheses is the uncertainty in the unit of the last digit. The mode number difference of the optical frequency comb is calculated using the HITRAN 2008 database [18]. The uncertainty is typically 10 kHz for transitions recorded with a signal-to-noise ratio exceeding 4. The linewidth is about 250 kHz dominated by the power broadening. Tables 1 and 2 do not include the R(5) transitions of H35Cl and H37Cl even though they lie in the tuning range of the spectrometer because the hyperfine structure is not resolved with the current spectral resolution. Pressure shift of the R(0) transition for H35Cl is measured in tens of millitorr and is less than the frequency uncertainty. The measured frequencies are fit to the Hamiltonian of Eq. (1) to yield T 1  T 0 ; eqQ 1 ; C Cl1 ; B1 ; D1 , and H1 for the vibrational excited state, whereas eqQ 0 ; C Cl0 ; B0 ; D0 ; H0 and L0 of the ground state is fixed at the values taken from the previous work [15]. The value of L1 of the vibrational excited state is also fixed at zero because of the lack of the high J transitions in the present measurement. The weights for fitting are equal among the measured frequencies even though the uncertainties differ. Some of the measured frequencies, those with asterisk in the Obs.-Cal. column, are not

weighted for fitting because two lines overlap within the frequency spectral resolution of the spectrometer. Table 3 lists the determined molecular constants together with the fixed constants. The number in parentheses is the uncertainty in the unit of the last digit. Discrepancies between the measured frequencies and the frequencies calculated from the determined constants are given in the last column of Tables 1 and 2. Those with the most overlapped lines excluded from the fit have opposite sign and magnitude, which is reasonable when the relative intensity is considered. This fact suggests that the frequency determination, assignments, and the fitting are reasonable. The standard deviations are 10.1 kHz for H35Cl and H37Cl, which is as much as the experimental uncertainty. Therefore, the model Hamiltonian is also appropriate for the present measurements. Magnetic hyperfine interactions between the hydrogen nucleus and the rotation and between the chlorine nucleus and the rotation were considered in the analysis of millimeter-wave spectroscopy [19], and the coupling constants have similar magnitude of 50 kHz. However, we include only the latter in the Hamiltonian because the former slightly splits the energy levels and only broadens spectral lines for the spectral resolution of the spectrometer. In contrast, the latter shifts the energy levels, which is significant for the accuracy of the frequency determination. The quadrupole and magnetic coupling constants in the vibrational excited state are determined at 69.301(12) MHz and 59.03(49) kHz for H35Cl. Those of the J = 1 level was determined at 69.272 89(93) MHz and 58.597(45) kHz from molecular-beam electric resonance spectra [8]. These are almost consistent within the uncertainties. 5. Summary We have recorded hyperfine-resolved spectra of the R(0) to R(4) transitions in the fundamental vibration band of H35Cl and H37Cl with a resolution of about 250 kHz. The absolute transition frequencies are measured with a typical uncertainty of 10 kHz. The crossover resonances enable us to determine all of the DF = 0, ±1 transition frequencies. Six molecular constants in the vibrational excited state are determined and the standard deviations of the fits are 10.1 kHz for H35Cl and H37Cl. Acknowledgments This work is supported by JSPS KAKENHI Grant No. 23244084, and the Photon Frontier Network Program of the Ministry of Education, Culture, Sports, Science and Technology, Japan. References [1] G.L. Villanueva, M.J. Mumma, R.E. Novak, Y.L. Radeva, H.U. Käufl, A. Smette, A. Tokunaga, A. Khayat, T. Encrenaz, P. Hartogh, Icarus 223 (2013) 11–27. [2] V.A. Krasnopolsky, D.A. Belyaev, I.E. Gordon, G. Li, L.S. Rothman, Icarus 224 (2013) 57–65. [3] A. Jones, K.A. Walker, J.J. Jin, J.R. Taylor, C.D. Boone, P.F. Bernath, S. Brohede, G.L. Manney, S. McLeod, R. Hughes, W.H. Daffer, Atmos. Chem. Phys. 12 (2012) 5207–5220. [4] D. Kreyling, H. Sagawa, I. Wohltmann, R. Lehmann, Y. Kasai, J. Geophys, Res.Atoms. 118 (2013) 11888–11903. [5] D. Hurtmans, A. Henry, A. Valentin, C. Boulet, J. Mol. Spectrosc. 254 (2009) 126–136. [6] C.P. Rinsland, M.A.H. Smith, A. Goldman, V.M. Devi, D.C. Benner, J. Mol. Spectrosc. 159 (1993) 274–278. [7] J.A. Coxon, P.G. Hajigeorgiou, J. Mol. Spectrosc. 203 (2000) 49–64. [8] E.W. Kaiser, J. Chem. Phys. 53 (1970) 1686–1703. [9] F.H. de Leluw, A. Dymanus, J. Mol. Spectrosc. 48 (1973) 427–445. [10] G. Jones, W. Gordy, Phys. Rev. 136 (1964) A 1229–A 1232. [11] F.C. De Lucia, P. Helminger, W. Gordy, Phys. Rev. A 3 (1971) 1849–1857. [12] I.G. Nolt, J.V. Radostitz, G. DiLonardo, K.M. Evenson, D.A. Jennings, K.R. Leopold, M.D. Vanek, L.R. Zink, A. Hinz, K.V. Chance, J. Mol. Spectrosc. 125 (1987) 274– 287. [13] H. Odashima, L.R. Zink, K.M. Evenson, J. Mol. Spectrosc. 194 (1999) 283–284. [14] Th. Klaus, S.P. Belov, G. Winnewisser, J. Mol. Spectrosc. 187 (1998) 109–117.

K. Iwakuni et al. / Journal of Molecular Spectroscopy 306 (2014) 19–25 [15] G. Cazzoli, C. Puzzarini, J. Mol. Spectrosc. 226 (2004) 161–168. [16] P. De Natale, L. Lorini, M. Inguscio, G. Di Lonardo, L. Fusina, Chem. Phys. Lett. 273 (1997) 253–258. [17] K. Iwakuni, S. Okubo, H. Sasada, Opt. Express 21 (2013) 14832–14840. [18] L.S. Rothman, I.E. Gordon, Y. Babikov, A. Barbe, D.C. Benner, P.F. Bernath, M. Birk, L. Bizzocchi, V. Boudon, L.R. Brown, A. Campargue, K. Chance, E.A. Cohen, L.H. Coudert, V.M. Devi, B.J. Drouin, A. Fayt, J.-M. Flaud, R.R. Gamache, J.J. Harrison, J.-M. Hartmann, C. Hill, J.T. Hodges, D. Jacquemart, A. Jolly, J.

25

Lamouroux, R.J. LeRoy, G. Li, D.A. Long, O.M. Lyulin, C.J. Mackie, S.T. Massie, S. Mikhailenko, H.S.P. Müller, O.V. Naumenko, A.V. Nikitin, J. Orphal, V. Perevalov, A. Perrin, E.R. Polovtseva, C. Richard, M.A.H. Smith, E. Starikova, K. Sung, S. Tashkun, J. Tennyson, G.C. Toon, Vl.G. Tyuterev, G. Wagner, J. Quant. Spectrosc. Radiat. Transfer 130 (2013) 4–50. [19] R.F. Code, A. Khosla, I. Ozier, N.F. Ramsey, P.N. Yi, J. Chem. Phys. 49 (1968) 1895–1901.