Peter F. Bernath and Robert W. Field- Optical-Optical Double-Resonance Spectroscopy of CaF

8/3/2019 Peter F. Bernath and Robert W. Field- Optical-Optical Double-Resonance Spectroscopy of CaF

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JOURNAL OF MOLECULAR SPECTROSCOPY 82, 339-347 (1980)

Optical-Optical Double-Resonance Spectroscopy of CaF

The E22+ and E 211 States

P E T E R F . BERNATH AND ROBERT W. FIELD

Department of Chemistry and Spectroscopy Laboratory, Massachusetts Institute of Technology,Cambridge, Massachusetts 02139

Optical-optical double-resonance (OODR) spectra of CaF are recorded, with reducedDoppler broadening, using two cw, single-mode dye lasers. Molecular constants for FP+and E VI are obtained from rotational analysis of the O-O and 1-O EZI+-A2n bandsand the O-O E *II-A*II band, supplemented by fragmentary observations on the E-A0- 1 and 1- 1 bands:

Main parametersEzz+ E *rI

TO 34 171.218(2) 34 477.413(3)AG,,z 640.912(3) 668.991(24)& 0.364393( 18) 0.368423(50)

f ; O)0.002266(18) 0.002375(50)

- 16.483(4)

The E *rl state is observed for the first time. Improved constants for the A% state areobtained by fitting all extant rotational and vibrational information for the E-A andA-X systems. The E and E states are found to obey the unique perturber rather than thepure precession relationship.

INTRODUCTION

Optical-optical double-resonance (OODR) excitation spectroscopy has provedto be a useful technique for the analysis of levels 3.4-4.5 eV above the groundstate in diatomic molecules [for example, (1, 2)]. OODR allows the automaticand unambiguous projection of an assignment of a visible wavelength spectrum

into the ultraviolet. This is particularly useful when convenient lasers for the directuv transition are lacking or when the direct transition is weak. In the case of CaFthis allows detection of the E 2J iI tate which has not been observed previously,probably due to weak oscillator strength of the El-X transition.

The use of two single-mode, cw dye lasers gives a substantial increase in signal-to-noise and resolution over broadband and/or pulsed dye lasers. Their large powerper unit bandwidth and stable operation make single-mode, cw lasers the lasersof choice for analysis of complex spectra. Linewidths are sub-Doppler, even formost lines arising from collision-induced rotational relaxation.

In the present OODR experiments the A211-XT analyses of Field et al. (3)and Nakagawa et al. (4) were used to assign the intermediate level populated

339 0022-2852/80/080339-09$02.00/OCopyright 0 1980 by Academic Press. Inc.

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340 BERNATH AND FIELD

TABLE I

CaF O-O E TI-ATl Observed and Calculated Line Positions (in cm-l)a

J Pie(J)

2 2 . 5

2 3 . 5

2 4 . 5

2 5 . 5

2 6 . 5

2 7 . 5

2 8 . 5

2 9 . 5

3 0 . 5

3 1 . 5

3 2 . 5

3 3 . 5

1 8 0 0 1 . 8 5 7 ( O)

0 0 3 . 3 4 6 ( 3 )

0 0 4 . 8 6 9 ( O )

0 0 6 . 4 3 5 ( - l )

o o c . o 4 1 ( - 3 )

1 7 9 6 7 . 7 4 2 ( - l ) 1 7 9 6 9 . 6 8 2 ( - l ) 0 0 9 . 6 9 3 ( l )

9 6 7 . 9 7 7 ( l ) 9 6 9 . 9 3 8 ( - 3 ) 0 1 1 . 3 8 1 ( O)

9 6 8 . 2 5 0 ( - l ) 9 7 0 . 2 4 0 ( - l ) 0 1 3 . 1 1 0 ( - 2 )

9 6 8 . 5 7 4 ( 7 ) 9 7 0 . 5 7 7 ( - l ) 0 1 4 . 8 8 5 ( O)

9 7 0 . 9 5 6 ( l ) 0 1 6 . 6 9 9 ( O )

0 1 8 . 5 5 6 ( l )

1 8 0 0 2 . 1 4 8 ( l )

0 0 3 . 6 2 8 ( 3 )

0 0 5 . 1 4 7 ( l )

0 0 6 . 7 0 8 ( 3 )

0 0 8 . 3 0 0 ( - 2 )

0 0 9 . 9 3 8 ( Z )

0 1 1 . 6 1 2 ( 2 )

0 1 3 . 3 2 4 ( - 3 )

0 1 5 . 0 6 9 ( - 3 )

0 1 6 . 8 5 9 ( - l )

0 1 8 . 6 8 8 ( l )

J PlSe(J T &( J )

1 3 . 5 1 7 8 9 6 . 7 8 0 ( - l )

1 4 . 5 8 9 6 . 3 6 1 ! - 3 ) 1 7 9 1 7 . 9 3 5 ( O )

1 5 . 5 8 9 5 . 9 7 1 ( - 4 )

J P p e W Ppf(J) R2,(J) R&J)

8 . 5 1 7 9 2 9 . 5 4 1 ( Z ) 1 7 9 2 9 . 6 0 7 ( 3 )

9 . 5 9 3 0 . 7 9 5 ( Z ) 9 3 0 . 8 8 0 ( 3 )

1 0 . 5 9 3 2 . 0 9 8 ( 3 ) 9 3 2 . 2 0 6 ( 4 )

1 1 . 5 9 3 3 . 4 4 4 ( - l ) 9 3 3 . 5 7 8 ( O)

1 2 . 5 9 3 4 . 8 4 0 ( - l ) 9 3 5 . 0 0 4 ( l )

1 3 . 5 9 3 6 . 2 8 1 ( - 3 ) 9 3 6 . 4 7 8 ( O )

1 4 . 5 1 7 9 1 5 . 3 0 9 ( 2 ) 9 3 7 . 7 7 1 ( - l ) 9 3 8 . 0 0 3 ( 2 )

1 5 . 5 9 1 5 . 3 5 3 ( - 3 ) 9 3 9 . 3 0 0 ( - 5 ) 9 3 9 . 5 7 4 ( 2 )

1 6 . 5 9 1 5 . 4 4 5 ( - 6 ) 9 4 0 . 8 7 7 ( - 5 ) 9 4 1 . 1 8 9 ( - l )

1 7 . 5 9 1 5 . 5 8 7 ( - 4 ) 9 4 2 . 8 5 7 ( l )

1 8 . 5 9 1 5 . 7 7 4 ( - 1 0 )

2 7 . 5 1 7 9 2 0 . 1 8 4 ( - 2 ) 9 6 1 . 0 0 6 ( 3 ) 9 6 1 . 9 5 2 ( - 4 )

2 8 . 5 9 1 9 . 9 6 5 ( O) 9 2 0 . 8 6 7 ( 4 ) 9 6 3 . 0 7 6 ( l ) 9 6 4 . 1 0 1 ( - 2 )

2 9 . 5 - 9 2 1 . 5 8 3 ( l ) 9 6 5 . 1 8 5 ( - l ) 9 6 6 . 2 9 1 ( O )

3 0 . 5 9 2 1 . 3 0 3 ( 6 ) 9 2 2 . 3 4 5 ( 2 )

3 1 . 5 9 2 2 . 0 2 5 ( 3 )

3 2 . 5 9 2 2 . 7 8 9 ( l )

' Br a c k e t e d n u mb e r s a r e ( o b s e r v e d - t a l c . ) i n 1 03 - 1

c m .


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CaF E*2+ AND E pII 341

TABLE II

CaF l- 1 E *i2-A*Il Observed and Calculated Line Positions (in cm-l)8

3 Pze(J) P2.(J) Rze(J) Q(J)

1 8 . 5 - 1 7 9 9 0 . 9 8 5 ( l )

1 9 . 5 - 9 9 1 . 2 5 7 ( - l ) 1 8 0 2 0 . 6 2 2 ( 5 ) 1 ( ; 0 2 0 . 9 9 6 ( - 1 3 )

2 0 . 5 - 9 9 1 . 5 7 8 ( l ) 0 2 2 . 3 6 9 ( 8 ) 0 2 2 . 7 9 3 ( - 7 )

2 1 . 5 - 9 9 1 . 9 4 7 ( 6 )

a Nu mb e r s i n p a r e n t h e s e s r e ( o h s e r v e d - t a l c . ) n 1 0 S 3 c m- ' .

TABLE III

CaF O-O EPC+-AW Observed and Calculated Line Positions (in cm-l)a

J

8 . 5

9 . 5

1 0 . 51 1 . 5

1 2 . 5

1 3 . 5

1 4 . 5

1 5 . 5

1 6 . 5

1 7 . 5

1 8 . 5

1 9 . 5

P,2(J)

1 7 5 9 7 . 9 8 0 ( - 2 )

5 9 7 . 2 1 6 ( - 4 )

5 9 6 . 4 8 8 ( O )

5 9 5 . 7 8 1 ( - 3 )

5 9 5 . \ 0 3 ( - 5 )

5 9 4 . 4 5 7 ( - 5 )

5 9 3 . 8 4 6 ( 2 ) .

5 9 3 . 2 6 3 ( 7 )

Q,(J)

1 7 6 1 1 . 2 5 4 ( O )

6 1 1 . 8 8 9 ( O )

6 1 2 . 5 5 0 ( - 2 )

6 1 3 . 2 3 8 ( - 6 )

6 1 3 . 9 6 5 ( l )

6 1 4 . 7 1 3 ( O )

6 1 5 . 4 8 8 ( - 2 )

6 1 7 . 1 2 8 ( - Z )

6 1 7 . 9 9 1 ( - 2 )

6 1 8 . 8 8 4 ( - l )

R12(J)

1 7 6 1 1 . 1 8 3 ( 6 )

6 1 1 . 8 4 5 ( 6 )

6 1 2 . 5 3 6 ( 6 )

6 1 3 . 2 3 8 ( - 1 0 )

6 1 4 . 0 0 0 ( 4 )

6 1 4 . 7 7 6 ( 4 )

6 1 5 . 5 8 0 ( 4 )

6 1 7 . 2 7 3 ( 2 )

6 1 8 . 1 6 0 ( - l )

6 1 9 . 0 8 1 ( - l )

J

2 4 . 5 1 7 6 0 7 . 0 9 1 ( 5 )

2 5 . 5 6 0 7 . 4 8 6 ( - 2 )

2 6 . 5 6 0 7 . 9 2 0 ( - l )

2 7 . 5 6 0 8 . 3 8 2 ( - l )

2 8 . 5 1 7 6 0 7 . 2 9 5 ( C) 6 0 8 . 8 7 1 ( - 4 )

2 9 . 5 6 0 7 . 7 5 4 ( O) 6 0 9 . 3 9 2 ( - 5 )

3 0 . 5 6 0 8 . 2 5 5 ( 5 )

' Nmb e r s i n p a r e n t h e s e s r e ( o h s . - t a l c . ) n l o - 3 c m- 1 .


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TABLE IV

CaF 1-O E*B+-ATI Observed and Calculated Line Positions (in cm-)a

J P,2(J) Q,(J) R,2(J)

9.5

1 0 . 5

1 1 . 5

1 2 . 5

1 3 . 5

1 4 . 5

1 5 . 5

1 6 . 5

1 7 . 5

1 8 . 5

1 9 . 5

1 8 2 3 8 . 7 0 2 ( - Z )

2 3 7 . 8 9 7 ( - l )

2 3 7 . 1 1 7 ( - l )

2 3 6 . 3 5 9 ( - 2 )

2 3 5 . 6 2 8 ( O )

2 3 4 . 9 2 2 ( 3 )

2 3 4 . 2 3 4 ( - l )

2 3 3 . 5 7 7 ( 2 )

2 3 2 . 9 4 5 ( 4 )

1 8 2 5 3 . 1 5 3 ( l )

2 5 3 . 7 8 7 ( - 2 )

2 5 4 . 4 5 0 ( O )

2 5 5 . 1 3 3 ( - l )

2 5 5 . 8 3 5 ( - 7 )

2 5 6 . 5 7 6 ( l )

2 5 7 . 3 3 3 ( l )

2 5 8 . 1 1 4 ( l )

2 5 8 . 9 0 5 ( - 1 4 )

1 8 2 5 3 . 1 0 9 ( 3 )

2 5 3 . 7 7 2 ( 5 )

2 5 4 . 4 5 0 ( - 4 )

255.894(-3)

256.659(4)2 5 7 . 4 4 3 ( 6 )

2 5 8 . 2 4 7 ( 4 )

2 5 9 . 0 6 9 ( - 4 )

J P2(J) Q,,(J) R2(J)

2 2 . 5 1 8 2 4 6 . 0 4 7 ( 2 )

2 3 . 5 2 4 6 . 3 0 6 ( - 3 )

2 4 . 5 2 4 6 . 5 7 3 ( O )

2 5 . 5 2 4 6 . 8 5 1 ( - 1 1 )

2 6 . 5 1 8 2 4 5 . 8 7 8 ( 6 )

2 7 . 5 2 4 6 . 1 6 4 ( 2 ) 2 4 7 . 5 2 5 ( 9 ) 1 8 2 8 7 . 1 8 5 ( - 1 0 )

2 8 . 5 2 4 6 . 4 8 2 ( 4 ) 2 4 7 . 8 8 6 ( 5 )

2 9 . 5 2 4 6 . 8 2 2 ( 2 ) 2 4 8 . 2 6 8 ( - 4 )

3 0 . 5 2 4 7 . 2 0 0 ( 1 2 ) 2 4 8 . 6 7 6 ( - 1 2 )

3 1 . 5 2 4 7 . 5 8 0 ( O )

a Nu mb e r s i n p a r e n t h e s e s a r e ( o b s e r v e d - t a l c . ) i n 1 0 - 3 c m- l .

by the first laser. Scanning the second laser and monitoring the undispersed uvfluorescence allowed us to observe an OODR excitation spectrum which includedtransitions into the E2Z+ and E' I tates. In addition to characterizing these states,the data were used to improve the A-X constants in a combined E'-A -X directapproach least-squares fit (5). To obtain a satisfactory fit, the model of (4)had to be changed by the introduction of an A_, onstant (centrifugal distortion ofthe spin-orbit constant) in both 211 states. The simultaneous fit of the X, A, ndE' tates includes the microwave-optical double-resonance data of Nakagawaet al. (4), their optical data, and our more accurate (by a factor of 4), but less exten-sive, optical data. This kind of global fit minimizes correlations between param-eters and improves, the physical meaning of constants [for example, (6)].


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CaF E*S+ AND E *II 343

TABLE V

Constants for u = 0 of X, A, E, and E States of CaF (in cm-)

XY + AZ l l E ' L + b E " R

T o0 . 0 1 6 5 2 9 . 6 8 9 ( l ) 3 4 1 7 1 . 2 1 6 ( 2 ) 3 4 4 7 7 . 4 1 3 ( 3 )

6 0 0 . 3 4 2 4 &l ( 5 ) 0 . 3 4 7 5 3 7 ( 7 ) 0 . 3 6 3 2 6 0 ( 1 3 ) 0 . 3 6 7 2 3 6 ( 1 1 )

0 0 4 . 5 x l o - 7 ( 7 ) 4 . 6 1 x 1 0 - 7 ( 7 ) 4 . 2 7 x 1 0 - 7 ( 1 3 ) 4 . 5 0 x 1 0 - 7 ( g )

y o1 . 3 0 x 1 0 - 3 c - 0 . 0 5 5 7 0 ( E )

p 0 - 0 . 0 4 4 5 4 ( E ) 0 . 0 5 3 0 4 ( 1 2 )

q o - 2 . 9 7 x W4 ( 6 ) 7 . 7 4 x 1 0 _ 4 ( 3 )

0 0 - 1 . 1 4 5 d 0 . 2 9 8 d

A, 7 1 . 4 5 0 ( l ) 1 6 . 4 8 3 ( 4 )

AJ 01 . 7 6 x 1 0 - 5 ( 1 2 ) - 6 . 7 1 Y 1 0 L 5 ( 3 6 )

' On e s t a n d a r d d e v i a t i o n e r r o r i s g i v e n i n p a r e n t h e s e s .

b Ad d e d f o r c a n p a r i s o n p u r p o s e s f r o m T a b l e V I .

' T h e X s t a t e v a l u e o f y . w a s f i x e d a t t h e HODR v a l u e o f ( A ) . T h i s v a l u e h a s b e e n c o n f i r m e d b y u s a th i g h J u s t n g s a t u r a t i o n s p e c t r o s c o p y . S i n c e t h e s p i n - r o t a t i o n s p l i t t i n g wa s o f t e n o n l y p a r t l yr e s o l v e d , v a r i a t i o n o f l o w o u l d h a v e b e e n h a z a r d o u s .

d F I x e d a t t h e u n i q u e p e r t u r b e r v a l u e o f $ 2 ) ~ .

EXPERIMENTAL DETAILS

CaF was produced by the Ca + SF, reaction in a Broida-type oven system(7). Argon was used as carrier gas and the pressure in the fluorescence regionwas typically 2 Torr. Only trace amounts of SF6 (el%), introduced in a concen-tric burner arrangement, were required to produce a CaF flame.

The first laser in the OODR excitation scheme, which transferred populationfrom x22+ to a selected A2ll rotation-vibration level, was a Coherent RadiationModel 599-21 dye laser operated with Rhodamine 6G dye. The second laser wasanother Model 599-2 1 but with Rhodamine 110 dye. Both dye lasers were excitedwith 514.5 nm radiation from a single CR-10 Ar+ laser. Frequency calibration ofeach dye laser was accomplished using an 1, reference cell and frequency markersfrom a 750-MHz free spectral range, half-confocal Fabry-Perot. This allowed linepositions to be measured to to.004 cm- using an I* atlas (8).

The experimental data were recorded by leaving the first laser fixed at the peakof a selected transition, unambiguously selecting a U J , and parity level of theA21I state. The exact location of this transition was determined by scanning thefirst laser and monitoring the total fluorescence with a Hamamatsu R372 photo-multiplier through a Ditric 610~nm (lo-nm bandpass) interference filter. TheA-X transitions were assigned by measuring the lines relative to I2 and thenusing a map of calculated line positions based on Nakagawas constants (4).

The second laser was combined with the first using a beam-splitter and thecopropagating beams were focused into the oven with a 12-in. focal length

* Wavenumbers from the I2 atlas used here (8) are too large by 0.0056 cm- [S. Gerstenhom andP. LUC, Rev. Phys. Appl. 14, 791-794 (1979)]. All CaF lines and band origins should be decreasedby this amount.


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T

BV

D"

YV

TABLE VI

CaF PI+ Consta nts (in cm-1)a

v= o v-l

3 4 1 7 1 . 2 1 8 ( 2 ) 3 4 8 1 2 . 1 3 0 ( 2 )

0 . 3 6 3 2 6 0 ( 1 3 ) 0 . 3 6 0 9 9 4 ( 1 2 )

4 . 2 7 x 1 0 - 7 ( 1 3 ) 3 . 8 8 x 1 0 - 7 ( 1 2 )

0 . 0 5 5 7 0 ( 8 ) 0 . 0 4 9 2 1 ( 8 )

AG~ , ~ = 6 4 0 . 9 1 2 ( 3 )

u e = 0 . 0 0 2 2 6 6 ( 1 8 )

' De t e r mi n e d r o m E - A f i t s wi t h A2 n c o n s t a n t s f i x e d a t t h e v a l u e s o f T a b l e V .Z e r o o f e n e r g y i s v = 0 o f X2 2 + s t a t e , a s i n T a b l e V. Un c e r t a i n t i e s np a r e n t h e s e sc o r r e s p o n d o o n e s t a n d a r d d e v i a t i o n .

lens. The second laser was scanned and the ultraviolet fluorescence was ob-served with a Hamamatsu R212 photomultiplier viewing through a Corning 7-54filter. For each level excited by the first laser, a series of l-cm-i scans coveringas much as 20 cm- was made with the second laser in order to observe as manycollisional satellites as possible. These lines appear because of collisional popula-tion of additional rotational levels in the A211 tate. They were assigned simply

by counting from the intense principal OODR line. In order to verify the vibra-tional and electronic assignments for the E and E' states, fluorescence intoATi was resolved for a few J values with a Spex Model 1802 l-m monochromator.

RESULTS

The unambiguous nature of laser double-resonance spectroscopy is balancedby the disadvantage that a large amount of work is required to generate andespecially to measure precise wavenumbers from high-resolution spectra. Sinceno perturbations were observed, good molecular constants can be derived from arelatively small set of high-quality measurements. Tables I-IV give the line posi-tions observed. The line positions of Table I were combined with O-O A-X dataof Nakagawaet d.(4) n a direct fit of E' 211(~ 0)-A211(v O)-XlI(v 0).The Hamiltonian used was the standard 211-2Z Hamiltonian (9). In order to ob-tain an adequate fit it was found necessary to introduce an AJ constant into the211 states. The constants obtained from the nonlinear least-squares fit are sum-marized in Table V. The E2Z+ v = 0 nd u = 1 constants, summarized in TableVI, were obtained by holding the A211 onstants fixed at the values of Table V.

In order to obtain AGIl values for the X and A states three lines of the 0- 1 E'211-A211 and were measured [P&23.5) 17330.856, P&24.5) 17331.475, R&22.5)17364.7181. Since term values are available from O-O and l-l A-X bands andthe O-O E'-A and, one gets AGl12 = 582.820(30) forXzZ+ and AG1,2 = 588.447(30)with the constants of (4) used for the 1- 1 A-X band. In addition, a few lines ofthe l- 1 E' 211-A211 and were also observed (Table II) and used in a least-squares fit to give AG,,, = 668.991(50) for E' 21'I. n this fit only E, nd B, were


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CaF FH+ AND E 211 345

TABLE VII

CaF E, A, and X Vibrational Constants (in cm-)a

X2 X + A- % E z r + E ' $

T e0 1 6 5 %. 7 5 ( l ) 3 4 1 4 1 . 7 7 ( 3 ) 3 4 4 6 3 . 6 0 ( 6 7 )

We5 8 8 . 8 7 ( E ) 5 9 4 . 8 6 ( 1 0 ) 6 4 8 . 0 3 ( 7 ) 6 7 5 . 4 9 0 3 0 )

v e3 . 0 8 ( 4 ) 3 . 2 6 ( 6 ) 3 . 6 1 ( 4 )

we x e ( P e k e r i s ) 3 . 1 4 ( 3 ) 3 . 2 7 ( 3 ) 2 . 9 5 ( Z ) 3 . 2 5 ( 6 )

" e y e0 . 0 3 3 ( 4 ) 0 . 0 3 9 ( 6 ) 0 . 0 3 3 ( 4 )

%n c e r t a i n t i e s i n p a r e n t h e s e s c o r r e s p o n d t o o n e s t a n d a r d d e v i a t i o n .

b Ad d e d f o r c n r p a r i s o n p u r p o s e s .T h e P e k e r i s v a l u e o f w x u s e d t o c a l c u l a t e T , a n dY f r o m T o a n d f f i l / 2 , i so f t e n a c c u r a t e t o % 2 0 %. T h i s e e &n a t e d e r r o r p r o p a g a t e s

i i % w e a n d T , .

allowed to vary with the other constants fixed (A, 16.363, p1 = 0.047, q1= 6.8 x 10e4, o1 = 0.263, A., = -6.7 x lo+, and D1 = 4.5 x 10-7) at valuesdetermined mainly by unique perturber relationships. Note that the o parameteris completely correlated with the band origin so its value affects the determinedAGllzs (as well as A, onstants).

These data can be used to determine the vibrational structure of the E, A, ndX states more accurately by combination with bandhead data of Fowler (IO) andJohnson (11) [Some small corrections in A-X assignments of (II) are givenin Rosens compilation (22).] The A-X band origins were estimated from Pzlbandheads using the vibrational dependence of spin-orbit and rotational con-stants given in (4) and holding the other parameters fixed at u = 0 values. Aweighted linear least-squares fit resulted in the constants given in Table VII. Thevibrational constants of the E22+ state (Table VII) were determined in a similarfashion from P, eads of E-X bands (10) but with the X-state vibrational con-stants fixed at the values determined from the A-X fit. Uncertainties of theband origins determined from bandheads were considered to be about 0.3 cm-(and weighted proportional to the reciprocal squared uncertainty) while the

rotationally analyzed band origins were weighted with the estimated la values.The fitted values of o,x, agree reasonably well with estimates based on thePekeris relationship (13) but the Pekeris value for the Z?Z+ state seems too low.The Pekeris relationship gives a value of o,x, = 3.25 cm- for the E' 211 tate.

DISCUSSION

The values of the constants derived for the X and A states of CaF agree wellwith those in (4). The X constants agree within quoted standard deviations butmany of our A-state constants lie just outside the standard deviations in (4).

* Vibrational constants of the CaF XI+ state have been redetermined from band origin dataalone [M. Duiick, P. Bemath, and R. W. Field, Canad. J. Phys. 58, 703-712 (1980)]. Agreementwith those constants is poor, presumably because the band head data (I I ) are less accurate than0.3 cm-*. The la uncertainties listed in Table VII should be increased by a factor of 4 for the X, A,and E states.


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Our introduction of AJ note, A, (14) AD/2 (9)] is responsible for this difference.Our value of A., s a factor of 6 larger than the value of A., omputed using theformula in (14). This is not too surprising because our A., s, to some extent,

phenomenological since it has absorbed various constants with similar matrixelements such as yn.

The electronic states of CaF are interesting because many of the transitionscan be interpreted in terms of a simple hydrogenic, one-electron picture. CaFbehaves like Ca+F- with the single nonbonding Ca+ valence electron responsiblefor all observed electronic transitions. For instance, the ATI and ES+ statesseem to be part of a 4p complex and, hence, obey Van Vlecks pure precessionrelations (15) with 1 = 1. For the E and E' tates a value of 1 = 1 would suggesty0 = p,, = 0.075. Th is value is about 40% too large; yet y0 = p,,. Consequently,these two states form a unique perturber pair (5) but with I no longer a goodquantum number. Using the complete summation definitions of rf, pf, and 40(5) but using only one pair of electronic states gives (ET%+ !+ E' I) = 1.220,1.191, and 0.961 from $, pt, and qf, respectively. The radial dependenceof A(R) has also been neglected but it is unimportant at this level of accuracy.

The change in o, from the ground-state value of 588.87 cm-l to 648.03 cm-lin the E state and 675.49 cm- in the E' state indicates that the nonbondingvalence electron is actually slightly antibonding. The R, value changes from1.95165 A in the X state to 1.89544 A in the E state and 1.88505 8, in the E'state. These W, and R, values confirm the expectation that the CaF+ species is

more tightly bound than CaF since (Rydberg-like) highly excited CaF stateswould resemble the ion.There is some evidence that the E' 'II-X'%+ ransition dipole moment is small.

The transition was not observed in absorption by Fowler (10) although he observedthe E*2+-XT transition (which he described as very weak). He did observesome extra features in this region but assigned them to impurity bands. In addition,we were never able to record rotationally resolved uv emission, which suggests thatthis emission cannot compete with other radiative channels. The El-A andEl-B ransitions could be observed easily in fluorescence and confirm the vibra-tional assignment of the E' tate. This displays a useful feature of OODR spec-troscopy. A weak direct transition in the ultraviolet region of the spectrum can beobserved via two strong transitions both in the visible region.

ACKNOWLEDGMENTS

P.F.B. was supported by a Canadian NSERC postgraduate scholarship and by National ScienceFoundation Grant CHE78-18427 and Air Force Office of Scientific Research Grant AFOSR-763056. Equipment utilized was provided by NSF Grant CHE75-19410. We would like to thank MichaelDulick for experimental assistance and Richard Gottscho for advice and the use of some of his computerprograms to fit the data.

RECEIVED: May 3, 1979

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4110-4122 (1978).


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CaF E 2P + AND E *I I 347

3. R. W. F IEL D, D. 0 . HARR IS, AND T. TANAKA, J . Mol. Spectrosc. 57, 107-117 (1975).4 . J . NAKAGAWA, P . J . DOMAILLE, T. C. STE IMLE , AN D D. 0. HAR RI S, . Mol. Spectrosc. 70 ,

374-385 (1978).5 . R . N. ZARE , A. L . SCH MELTEKOP F, . J . HARROP , AND D. L . ALBR ITTO N, I . Mol. Spectrosc.

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164-168 (1975).8 . S . GER~TENKORN AN D P . L u c , At l a s d u s p e c t r e d a b s o r p t i o n d e la m o l t c u l e d i o d e ,

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Peter F. Bernath and Robert W. Field- Optical-Optical Double-Resonance Spectroscopy of CaF

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